- focus
- 1644, from L. focus "hearth, fireplace," 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 1604, but it is not recorded). Introduced into Eng. 1656 by Hobbes. Sense transfer to "center of activity or energy" is first recorded 1796. The verb is first attested 1814 in the literal sense; the fig. sense is recorded earlier (1807).