noun, plural fo·cus·es, fo·ci [foh-sahy, -kahy] /ˈfoʊ saɪ, -kaɪ/.
- the focal point of a lens, on which rays converge or from which they deviate.
- the focal length of a lens; the distance from a focal point to a corresponding principal plane.
- the clear and sharply defined condition of an image.
- the position of a viewed object or the adjustment of an optical device necessary to produce a clear image: in focus; out of focus.
verb (used with object), fo·cused, fo·cus·ing or (especially British) fo·cussed, fo·cus·sing.
verb (used without object), fo·cused, fo·cus·ing or (especially British) fo·cussed, fo·cus·sing.
Origin of focus
Synonyms for focus
noun plural -cuses or -ci (-saɪ, -kaɪ, -kiː)
verb -cuses, -cusing, -cused, -cusses, -cussing or -cussed
Word Origin for focus
1640s, from Latin focus "hearth, fireplace" (also, figuratively, "home, family"), of unknown origin, used in post-classical times for "fire" itself, taken by Kepler (1604) in a mathematical sense for "point of convergence," perhaps on analogy of the burning point of a lens (the purely optical sense of the word may have existed before Kepler, but it is not recorded). Introduced into English 1650s by Hobbes. Sense transfer to "center of activity or energy" is first recorded 1796.
1775 in the literal sense; 1807 in the figurative sense, from focus (n.). Related: Focused; focusing; less commonly focussed; focussing.