n. & v.
n. (pl. focuses or foci) 1 Physics a the point at which rays or waves meet after reflection or refraction. b the point from which diverging rays or waves appear to proceed. Also called focal point. 2 a Optics the point at which an object must be situated for an image of it given by a lens or mirror to be well defined (bring into focus). b the adjustment of the eye or a lens necessary to produce a clear image (the binoculars were not in focus). c a state of clear definition (the photograph was out of focus). 3 the centre of interest or activity (focus of attention). 4 Geom. one of the points from which the distances to any point of a given curve are connected by a linear relation. 5 Med. the principal site of an infection or other disease. 6 Geol. the place of origin of an earthquake.
v. (focused, focusing or focussed, focussing) 1 tr. bring into focus. 2 tr. adjust the focus of (a lens, the eye, etc.). 3 tr. & intr. (often foll. by on) concentrate or be concentrated on. 4 intr. & tr. converge or make converge to a focus. focuser n.
[ L, = hearth ]