■ noun ( plural ~es or foci 'fəʊsʌɪ )
1》 the centre of interest or activity.
↘an act of ~ing on something.
2》 the state or quality of having or producing clear visual definition.
↘another term for focal point .
↘the point at which an object must be situated with respect to a lens or mirror for an image of it to be well defined.
3》 Geology the point of origin of an earthquake. Compare with epicentre .
4》 Medicine the principal site of an infection or other disease.
5》 Geometry one of the fixed points from which the distances to any point of an ellipse, parabola, or other curve are connected by a linear relation.
6》 Linguistics an element of a sentence that is given prominence by intonational or other means.
■ verb ( ~es , ~ing , ~ed or ~ses , ~sing , ~sed )
1》 adapt to the prevailing level of light and become able to see clearly.
↘adjust the ~ of (a telescope, camera, etc.).
↘(of rays or waves) meet at a single point.
↘(of light, radio waves, or other energy) become concentrated into a sharp beam of light or energy.
2》 ( ~ on ) pay particular attention to.
3》 Linguistics place the ~ on (a part of a sentence).
Derivatives
~er noun
Origin
C17: from L., lit. 'domestic hearth'.