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n. pl. fo·cus·es or fo·ci (-sī′, -kī′)
a. The distinctness or clarity of an image rendered by an optical system.
b. The state of maximum distinctness or clarity of such an image: in focus; out of focus.
c. 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.
a. 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.
a. A center of interest or activity: "Precisely how diet affects E. coli in livestock is the focus of current research" (Cindy Engel).
b. 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).
c. A condition in which something can be clearly apprehended or perceived: couldn't get the problem into focus.
4. Medicine The region of a localized bodily infection or disease.
5. Geology The point of origin of an earthquake.
6. Mathematics A fixed point whose relationship with a directrix determines a conic section.
v. fo·cused, fo·cus·ing, fo·cus·es or fo·cussed or fo·cus·sing or fo·cus·ses
1. To cause (light rays, for example) to converge on or toward a central point; concentrate.
a. 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.
b. To adjust (a lens, for example) to produce a clear image.
3. To direct toward a particular point or purpose: focused all their attention on finding a solution to the problem.
1. To converge on or toward a central point of focus; be focused.
2. To adjust one's vision or an optical device so as to render a clear, distinct image.
3. To concentrate attention or energy: a campaign that focused on economic issues.

[New Latin, from Latin, hearth (probably in reference to the fact that a lens or parabolic mirror can concentrate sunlight on a single point to start a fire).]

fo′cus·er n.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.focussing - the concentration of attention or energy on something; "the focus of activity shifted to molecular biology"; "he had no direction in his life"
engrossment, immersion, absorption, concentration - complete attention; intense mental effort
particularism - a focus on something particular
References in classic literature ?
There was such a focussing of factors that the whole matter appeared to have been previously rehearsed.
whole pages of it are filled with masses of figures, generally single numbers added up in batches, and then the totals added in batches again, as though he were focussing some account, as the auditors put it.
Thus, although we found Southampton full of Pressmen, we absolutely refused to give any information, which had the natural effect of focussing public attention upon the meeting which was advertised for the evening of November 7th.