For the noun: focus
Plural form: focuses, foci

WordReference Random House Learner's Dictionary of American English © 2015
fo•cus /ˈfoʊkəs/USA pronunciation n., pl. -cus•es, -ci/-saɪ, -kaɪ/USA pronunciationv., -cused, -cus•ingor (esp. Brit.)-cussed, -cus•sing.

  • [countable] a central point, such as of attraction, attention, or activity:His focus was on earning a living.
  • Physics[countable] a point at which rays of light, heat, or other radiation meet after being refracted or reflected.
  • Optics[uncountable] the adjustment of an optical device that is necessary to produce a clear image:The image is in focus.

  • v. 
  • to (cause to) come to a focus or into focus: [+ object]to focus the lens of a camera.[no object]For a few moments my eyes wouldn't focus.
  • to concentrate: [+ object]I tried to focus my thoughts.[no object; (~ + on + object)]I tried to focus on the project.

  • Collins Concise English Dictionary © HarperCollins Publishers::

    focus /ˈfəʊkəs/ n ( pl -cuses, -ci / -saɪ -kaɪ -kiː/)
    1. a point of convergence of light or other electromagnetic radiation, particles, sound waves, etc, or a point from which they appear to diverge
    2. another name for focal point, focal length
    3. the state of an optical image when it is distinct and clearly defined or the state of an instrument producing this image: the picture is in focus, the telescope is out of focus
    4. a point upon which attention, activity, etc, is directed or concentrated
    5. a fixed reference point on the concave side of a conic section, used when defining its eccentricity
    6. the point beneath the earth's surface at which an earthquake or underground nuclear explosion originates
      Compare epicentre
    7. the main site of an infection or a localized region of diseased tissue
    vb ( -cuses, -cusing, -cused, -cusses, -cussing, -cussed)
    1. to bring or come to a focus or into focus
    2. (transitive) often followed by on: to fix attention (on); concentrate
    Etymology: 17th Century: via New Latin from Latin: hearth, fireplace

    ˈfocuser n

    'focus' also found in these entries:

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