red-

Multiple Entries:
  red-    re-  

Concise Oxford English Dictionary © 2008 Oxford University Press:
red-

▶prefix variant of re- before a vowel (as in redolent).

Concise Oxford English Dictionary © 2008 Oxford University Press:
re-/riː/

▶prefix

• 1 once more; afresh; anew: reactivate.

  ■ with return to a previous state: restore.

• 2 (also red-) in return; mutually: resemble.

  ■ in opposition: repel.

• 3 behind or after: relic.

  ■ in a withdrawn state: reticent.

  ■ back and away; down: recede.

• 4 with frequentative or intensive force: resound.

• 5 with negative force: recant.

– origin from L. re-, red- ‘again, back’.

usage: Words formed with re- tend to be unhyphenated: restore, reacquaint. An exception to this occurs when the word to which re- attaches begins with e, in which case a hyphen is often inserted for clarity: re-examine, re-enter. A hyphen is sometimes also used where the word formed with the prefix would be identical to an already existing word: re-cover (meaning ‘cover again’) not recover (meaning ‘get better in health’).