[fo.cus] n, pl fo.ci also fo.cus.es [NL, fr. L, hearth] (1644) 1 a: a point at which rays (as of light, heat, or sound) converge or from which they diverge or appear to diverge; specif: the point where the geometrical lines or their prolongations conforming to the rays diverging from or converging toward another point intersect and give rise to an image after reflection by a mirror or refraction by a lens or optical system b: a point of convergence of a beam of particles (as electrons)
2. a: focal length b: adjustment for distinct vision; also: the area that may be seen distinctly or resolved into a clear image c: a state or condition permitting clear perception or understanding "tried to bring the issues into ~" d: direction 6c
3: one of the fixed points that with the corresponding directrix defines a conic section
4: a localized area of disease or the chief site of a generalized disease or infection
5. a: a center of activity, attraction, or attention "the ~ of the meeting was drug abuse" b: a point of concentration
6: the place of origin of an earthquake or moonquake 7: directed attention: emphasis -- fo.cus.less adj -- in focus : having or giving the proper sharpness of outline due to good focusing -- out of focus : not in focus
[2]focus vb fo.cused also fo.cussed ; fo.cus.ing also fo.cus.sing vt (1775) 1 a: to bring into focus b: to adjust the focus of (as the eye or a lens)
2: to cause to be concentrated "~ed their attention on the most urgent problems"
3: to bring (as light rays) to a focus: concentrate ~ vi 1: to come to a focus: converge
2: to adjust one's eye or a camera to a particular range
3: to concentrate attention or effort -- fo.cus.able adj -- fo.cus.er n