—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.
Derivatives:
focuser n.
Etymology: L, = hearth
Useful english dictionary. 2012.