nounWord forms: plural -cuses or -ci (-saɪ, -kaɪ, -kiː)1. a point of convergence of light or other electromagnetic radiation, particles, sound waves, etc, or a point from which they appear to diverge
2. another name for focal point (sense 1), focal length
3. optics the state of an optical image when it is distinct and clearly defined or the state of an instrument producing this image
the picture is in focus
the telescope is out of focus
4. a point upon which attention, activity, etc, is directed or concentrated
5. geometry a fixed reference point on the concave side of a conic section, used when defining its eccentricity
6. the point beneath the earth's surface at which an earthquake or underground nuclear explosion originates
Compare epicentre 7. pathology the main site of an infection or a localized region of diseased tissue
verbWord forms: -cuses, -cusing, -cused, -cusses, -cussing or -cussed8. to bring or come to a focus or into focus
9. (transitive; often foll by on) to fix attention (on); concentrate
Word origin
C17: via New Latin from Latin: hearth, fireplace