WordReference Random House Learner's Dictionary of American English © 2019
back•up /ˈbækˌʌp/USA pronunciation   n. 
  1. [countable] a person or thing that supports;
  2. [uncountable] an accumulation due to stoppage.
  3. Mechanical Engineeringan alternate or substitute kept in reserve: [countable]She kept her original disks and her backups in a safe place.[uncountable]What backup do you have in case the power fails?

WordReference Random House Unabridged Dictionary of American English © 2019
back•up  (bakup′),USA pronunciation n. 
  1. a person or thing that supports or reinforces another.
  2. Music and Dancea musician or singer or group of musicians or singers accompanying a soloist:a singer with a three-man backup that plays cello, bass, and guitar.
  3. an overflow or accumulation due to stoppage, malfunctioning, etc.:a sewage backup; a backup of cars at the tollbooth.
  4. Mechanical Engineeringa person, plan, device, etc., kept in reserve to serve as a substitute, if needed.
  5. Computing
    • a copy or duplicate version, esp. of a file, program, or entire computer system, retained for use in the event that the original is in some way rendered unusable.
    • a procedure to follow in such an event.
  6. Sport[Bowling.]a ball that curves in a direction corresponding to the bowling hand of the bowler.

  1. Mechanical Engineering(of a person, plan, device, etc.) held in reserve as a substitute if needed:a backup driver; a backup generator.
  2. Music and Danceperforming a secondary or supporting function:A drummer and guitarist are the singer's backup musicians.
  • noun, nominal use of verb, verbal phrase back up 1775–85, American.

WordReference Random House Learner's Dictionary of American English © 2019
back1 /bæk/USA pronunciation   n. 
  1. the rear part of the human body from the neck to the end of the spine.
  2. Anatomythe part of an animal's body corresponding to the human back:stroked her dog on the back.
  3. the part that forms the back or reverse of an object or structure:I sat at the back of the room.
  4. the spine;
    backbone: broke his back.
    • a player, as in football, stationed to the rear of front-line play.

  1. [ + obj] to support, as with money: We'll back his plan if you do.
  2. [ + obj] to bet on: to back a horse in a race.
  3. to (cause to) move backward: [no obj ]:She backed slowly into the garage.[ + obj]:He backed the truck to the platform.
  4. [ + obj] to furnish with or be a back for:backed the picture with cardboard.
  5. [ + onto + obj] to lie at the back of something:The house backs onto the river.
  6. back down or off, [no obj ] to give up an argument or position:backed down from her stubborn refusal.
  7. back out, [no obj ] to fail to keep a promise;
    withdraw:Don't try to back out of the deal.
  8. back up,
    • to bring or come to a complete stop or standstill: [ + up + obj;
      usually passive]:Traffic is backed up to the bridge.[no obj ]:Traffic backed up quickly because of the accident.
    • to (cause to) become clogged due to a stoppage: [no obj]:The sink backs up almost every week.[ + up + obj]:That garbage will back up your septic tank.
    • Computing[ + up + obj ] to copy (a computer file or program) as a precaution against failure.

  1. [before a noun] situated at or in the rear:the back door.
  2. [before a noun] far away;
    remote:The farmer didn't plant the back pasture.
  3. [before a noun] of or belonging to the past: the back issues of a magazine.
  4. [before a noun] owed from an earlier time;
    overdue: She was rehired and given back pay.

  1. at, to, or toward the rear;
    backward: Please step back.
  2. in, at, or toward an original starting place, time, or condition: He went back to his home town. Put your coat back on.
  1. back and forth,
    • backward and forward;
      to and fro:pacing back and forth while I waited for the news.
  2. Idioms behind one's back, without one's knowledge;
    They talked about me behind my back.
  3. Idioms get one's back up, [no obj] to become annoyed;
    take offense:Don't get your back up; it was just a joke.
  4. go back on, [ + obj]
    • to fail to keep:Several times he went back on his word.
    • to be disloyal to;
      betray:She went back on her friend.
  5. Idioms (in) back of, at the rear of;
    behind:There's a small garden in back of the house.

    Although some people object to the use of in back of with the meaning "behind,'' it is fully established as standard in American English and appears in all types of speech and writing: The car was parked in back of the house.

WordReference Random House Unabridged Dictionary of American English © 2019
back1  (bak),USA pronunciation n. 
  1. Anatomythe rear part of the human body, extending from the neck to the lower end of the spine.
  2. Anatomythe part of the body of animals corresponding to the human back.
  3. the rear portion of any part of the body:the back of the head.
  4. the whole body, with reference to clothing:the clothes on his back.
  5. ability for labor;
    endurance:He put his back into the task.
  6. the part opposite to or farthest from the front;
    the rear part:the back of a hall.
  7. the part that forms the rear of any object or structure:the back of a chair.
  8. the part that covers the back:the back of a jacket.
  9. the spine or backbone:The fall broke his back.
  10. any rear part of an object serving to support, protect, etc.:the back of a binder.
  11. Nautical, Naval Termsthe forward side of a propeller blade (opposed to face).
  12. [Aeron.]the top part or upper surface of an aircraft, esp. of its fuselage.
  13. [Bookbinding.]the edge of a book formed where its sections are bound together.
  14. the backs, grounds along the River Cam in back of certain colleges at Cambridge University in England: noted for their great beauty.
  15. Architectureextrados.
  16. [Carpentry.]
    • Buildingthe upper side of a joist, rafter, handrail, etc.
    • Buildingthe area of interior wall between a window stool and the floor.
  17. Miningthe roof of a stope or drift.
  18. Sport
    • a player whose regular position is behind that of players who make initial contact with the opposing team, as behind the forward line in football or nearest the player's own goal in polo.
    • the position occupied by this player.
  19. Idiomsbe flat on one's back: 
    • Idiomsto be helpless or beaten:He's flat on his back after a long succession of failures.
    • Idiomsto be confined to one's bed because of illness.
  20. Idiomsbehind one's back, in one's absence;
    without one's knowledge;
    secretly:I'd rather talk to him about it directly than discuss it behind his back.
  21. Idiomsbreak someone's back, to cause a person to fail, esp. to cause to become bankrupt:His family's extravagance is breaking his back.
  22. Idiomsbreak the back of: 
    • to complete the principal or hardest part of (a project, one's work, etc.):He finally broke the back of the problem.
    • to overcome;
      defeat:They broke the back of our union.
  23. Idioms, Informal Termsget off one's back, [Informal.]to cease to find fault with or to disturb someone:The fight started when they wouldn't get off my back.
  24. Informal Terms, Idiomsget one's back up, to become annoyed;
    take offense:She gets her back up whenever someone mentions her family's influence.
  25. Idiomshave one's back to the wall, to be in a difficult or hopeless situation.
  26. Idiomsin back of, behind:He hid in back of the billboard. What could be in back of his strange behavior?Also,  back of. 
  27. Informal Terms, Idiomson one's back, finding fault with or disturbing someone:The boss is always on my back about promptness.
  28. Idiomspat on the back. See  pat 1 (defs. 6, 10).
  29. Idiomsstab in the back. See  stab (def. 13).
  30. Idiomsturn one's back on: 
    • to forsake or neglect:He was unable to turn his back on any suffering creature.
    • to leave behind, as in anger.

  1. to support, as with authority, influence, help, or money (often fol. by up):to back a candidate; to back up a theory with facts.
  2. to bet on:to back a horse in the race.
  3. to cause to move backward (often fol. by up):to back a car.
  4. to furnish with a back:to back a book.
  5. to lie at the back of;
    form a back or background for:a beach backed by hills.
  6. to provide with an accompaniment:a singer backed by piano and bass.
  7. to get upon the back of;
  8. to write or print on the back of;
  9. [Carpentry.]to attach strips of wood to the upper edge of (a joist or rafter) to bring it to a desired level.
  10. Nautical, Naval Terms
    • to alter the position of (a sail) so that the wind will strike the forward face.
    • to brace (yards) in backing a sail.
    • to reinforce the hold of (an anchor) by means of a smaller one attached to it and dropped farther away.

  1. to go or move backward (often fol. by up).
  2. Nautical(of wind) to change direction counterclockwise (opposed to veer).
  3. Nauticalback and fill: 
    • Naval Terms[Naut.]to trim the sails of a boat so that the wind strikes them first on the forward and then on the after side.
    • Idiomsto change one's opinion or position;
  4. Dialect Terms, Idiomsback and forth, [South Midland U.S.]
    • to go back and forth, as in running errands or visiting:He spent the day backing and forthing to the post office.
    • to work in an aimless or ineffective way;
      expend effort with little result.
  5. back away, to retreat;
    withdraw:They gradually began to back away from their earlier opinion.
  6. back down, to abandon an argument, opinion, or claim;
    retreat:He backed down as soon as a member of the audience challenged his assertion.
  7. back off: 
    • to back down:Now that the time for action had arrived, it was too late to back off.
    • Textilesto reverse (the spindle) in mule spinning prior to winding on the newly spun length of yarn.
  8. back out or  out of, to fail to keep an engagement or promise;
    withdraw from;
    abandon:Two entrants have backed out of competing in the marathon. You can't back out now.
  9. back up: 
    • to bring (a stream of traffic) to a standstill:A stalled car backed up traffic for miles.
    • [Printing.]to print a sheet again on its other side.
    • [Printing.]to fill in (the thin copper shell of an electrotype) with metal in order to strengthen it.
    • to move backward:Back up into the garage.
    • to reinforce:We backed up the cardboard with slats so it wouldn't fall down.
    • to support or confirm:He backed up my story and they let us go.
    • Computingto duplicate (a file or a program) as a precaution against failure.
  10. back up for, [Australian Informal.]to return for more of, as another helping of food.
  11. Nauticalback water: 
    • [Naut.]to reverse the direction of a vessel.
    • Idiomsto retreat from a position;
      withdraw an opinion:I predict that the council will back water on the tax issue.

  1. situated at or in the rear:at the back door; back fence.
  2. far away or removed from the front or main area, position, or rank;
    remote:back settlements.
  3. belonging to the past:back files; back issues.
  4. in arrears;
    overdue:back pay.
  5. coming or going back;
    moving backward:back current.
  6. Nautical, Naval Terms[Navig.]reciprocal (def. 7).
  7. Phonetics(of a speech sound) produced with the tongue articulating in the back part of the mouth, as in either of the sounds of go.
backless, adj. 
  • Indo-European *bhogo- bending; compare bacon
  • bef. 1000; Middle English bak, Old English bæc back of the body; cognate with Old Frisian bek, Old Saxon, Old Norse bak; perh.
    • 31.See corresponding entry in Unabridged sustain, abet, favor, assist;
      countenance, endorse.
    • 41.See corresponding entry in Unabridged retire, retreat, withdraw.
    • 52.See corresponding entry in Unabridged Back, hind, posterior, rear refer to something situated behind something else.
      Back means the opposite of front:back window.Hind, and the more formal word
      posterior, suggest the rearmost of two or more often similar objects:hind legs; posterior lobe.Rear is used of buildings, conveyances, etc., and in military language it is the opposite of fore:rear end of a truck; rear echelon.
    • 1, 52.See corresponding entry in Unabridged front.
    26. Although some object to their use, the phrases in back of and the shorter--and much older--back of with the meaning "behind'' are fully established as standard in American English:The car was parked(in) back of the house. Both phrases occur in all types of speech and writing.

back2  (bak),USA pronunciation adv. 
  1. at, to, or toward the rear;
    backward:to step back.
  2. in or toward the past:to look back on one's youth; They met in Chicago back in 1976.
  3. at or toward the original starting point, place, or condition:to go back to the old neighborhood.
  4. in direct payment or return:to pay back a loan; to answer back.
  5. in a state of restraint or retention:to hold back the tears; to hold back salary.
  6. in a reclining position:to lean back; to lie back.
  7. Idiomsback and forth, from side to side;
    to and fro;
    from one to the other:The pendulum of the grandfather clock swung back and forth.
  8. Dialect Terms, Idiomsback yonder, [Chiefly South Midland U.S.]formerly;
    many years ago:Back yonder, when I was a boy, things were different.
  9. go back on: 
    • to be treacherous or faithless to;
      betray:to go back on friends.
    • to fail to keep;
      renege on:to go back on promises.
  • aphetic variant of aback 1480–90

back3  (bak),USA pronunciation n. 
  1. a large tub, vat, or cistern used by dyers, brewers, distillers, etc., to hold liquids.
  2. a broad-beamed ferryboat hauled across a body of water by a rope or chain.
  • Late Latin bacca water container; compare French bac ferryboat, punt. See basin.
  • Dutch bak tub, trough
  • 1685–95

Collins Concise English Dictionary © HarperCollins Publishers::

back up vb (adverb)
  1. (transitive) to support or assist
  2. (intransitive) (of a nonstriking batsman) to move down the wicket in readiness for a run as a ball is bowled
  3. (of water) to accumulate
  4. (of traffic) to become jammed behind an accident or other obstruction
  5. to make a copy of (a data file), esp for storage in another place as a security copy
  6. to print the second side of (a sheet)
  7. (intr,) usually followed by on: Austral to repeat an action immediately
n backup
  1. a support or reinforcement
  2. a reserve or substitute
  3. (as modifier): backup troops
  4. US Canadian musical accompaniment, esp for a pop singer
  5. (as modifier): backup singer
  6. the overflow from a blocked drain or pipe

'backup' also found in these entries:

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