the rate or range of occurrence or influence of something, esp. of something unwanted

the high incidence of heart disease in men over 40.

a falling upon, affecting, or befalling; occurrence

The incidence of murder that Sunday afternoon shocked the sleepy village.

Optics, Physics .

the striking of a ray of light, beam of electrons, etc., on a surface, or the direction of striking.

angle of incidence ( def. 1 ) .

the fact or the manner of being incident.

Geometry . partial coincidence of two figures, as of a line and a plane containing it.

noun

frequency , rate , degree , number , extent , percentage , proportion , measure , scope , commonness , prevalence , tendency , trend , driftnotes:the primary meaning of incident is that of occurrence or event; the primary meaning of incidence is that of the rate or number of times at which something occurs