from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system: the focus of a lens. Also called focal point.
  • n. See focal length.
  • n. The distinctness or clarity of an image rendered by an optical system.
  • n. The state of maximum distinctness or clarity of such an image: in focus; out of focus.
  • n. An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear: a camera with automatic focus.
  • n. A center of interest or activity. See Synonyms at center.
  • n. Close or narrow attention; concentration: "He was forever taken aback by [New York's] pervasive atmosphere of purposefulness—the tight focus of its drivers, the brisk intensity of its pedestrians” ( Anne Tyler).
  • n. A condition in which something can be clearly apprehended or perceived: couldn't get the problem into focus.
  • n. Pathology The region of a localized bodily infection or disease.
  • n. Geology The point of origin of an earthquake.
  • n. Mathematics A fixed point whose relationship with a directrix determines a conic section.
  • transitive v. To cause (light rays, for example) to converge on or toward a central point; concentrate.
  • transitive v. To render (an object or image) in clear outline or sharp detail by adjustment of one's vision or an optical device; bring into focus.
  • transitive v. To adjust (a lens, for example) to produce a clear image.
  • transitive v. To direct toward a particular point or purpose: focused all their attention on finding a solution to the problem.
  • intransitive v. To converge on or toward a central point of focus; be focused.
  • intransitive v. To adjust one's vision or an optical device so as to render a clear, distinct image.
  • intransitive v. To concentrate attention or energy: a campaign that focused on economic issues.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. a point at which reflected or refracted rays of light converge.
  • n. a point of a conic at which rays reflected from a curve or surface converge.
  • n. The fact of the convergence of light on the photographic medium.
  • n. The quality of the convergence of light on the photographic medium.
  • n. concentration of attention.
  • n. the exact point of where an earthquake occurs, in three dimensions.
  • n. The indicator of the currently active element in a user interface.
  • n. The most important word or phrase in a sentence or passage, or the one that imparts information
  • v. To cause (rays of light, etc) to converge at a single point.
  • v. To adjust (a lens, an optical instrument) in order to position an image with respect to the focal plane.
  • v. To concentrate one's attention.
  • v. To make (a liquid) less diluted.
  • v. To concentrate one’s attention.

from the GNU version of the Collaborative International Dictionary of English

  • n. A point in which the rays of light meet, after being reflected or refracted, and at which the image is formed
  • n. A point so related to a conic section and certain straight line called the directrix that the ratio of the distance between any point of the curve and the focus to the distance of the same point from the directrix is constant.
  • n. A central point; a point of concentration.
  • transitive v. To bring to a focus; to focalize; as, to focus a camera.

from The Century Dictionary and Cyclopedia

  • To bring or adjust to a focus; cause to be in focus; focalize; collect in one point; concentrate.
  • n. In optics, a point at which rays of light that originally diverged from one point meet again, or a point from which they appear to proceed.
  • n. In geometry, a point from which the distances to any point of a given curve are in a syzygetic relation.
  • n. In the theory of perspective, with reference to two planes in perspective, one of four points—two, F1 and F2, on one plane, and two, f1 and f2, on the other—such that the angles between two points on the first plane measured at F1 are equal to the angles between the corresponding points on the other plane measured at f1, and so with the pair of foci F2 and f2.
  • n. Figuratively (with a consciousness of the classical Latin meaning), a central or gathering point, like the fire or hearth of a household; the point at or about which anything is concentrated; a center of interest or attraction.
  • n. In pathology, a center of morbid action; one of the primary or principal lesions.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a point of convergence of light (or other radiation) or a point from which it diverges
  • n. the concentration of attention or energy on something
  • n. maximum clarity or distinctness of an idea
  • n. maximum clarity or distinctness of an image rendered by an optical system
  • n. a central point or locus of an infection in an organism
  • v. direct one's attention on something
  • v. put (an image) into focus
  • n. a fixed reference point on the concave side of a conic section
  • v. become focussed or come into focus
  • v. cause to converge on or toward a central point
  • v. bring into focus or alignment; to converge or cause to converge; of ideas or emotions
  • n. special emphasis attached to something


Latin, hearth.
(American Heritage® Dictionary of the English Language, Fourth Edition)
Latin focus ("hearth, fireplace"), of unknown origin. Usually connected with Old Armenian բոց (bocʿ). (Wiktionary)



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    December 15, 2006