INCIDENCE

incidence

(noun) the striking of a light beam on a surface; “he measured the angle of incidence of the reflected light”

incidence, relative incidence

(noun) the relative frequency of occurrence of something

Source: WordNet® 3.1

Etymology

Noun

incidence (countable and uncountable, plural incidences)

The act of something happening; occurrence.

The extent or the relative frequency of something happening.

The manner of falling; bearing or onus, as of a tax that falls unequally.

(physics) The striking of radiation or a projectile upon a surface.

(epidemiology) A measure of the risk of a person developing a new condition within a specified period of time, usually a year.

(geometry) The falling of a point on a line, or a line on a plane.

Source: Wiktionary

In"ci*dence, n. Etym: [Cf. F. incidence.]

1. A falling on or upon; an incident; an event. [Obs.] Bp. Hall.

2. (Physics)

Definition: The direction in which a body, or a ray of light or heat, falls on any surface. In equal incidences there is a considerable inequality of refractions. Sir I. Newton. Angle of incidence, the angle which a ray of light, or the line of incidence of a body, falling on any surface, makes with a perpendicular to that surface; also formerly, the complement of this angle.

– Line of incidence, the line in the direction of which a surface is struck by a body, ray of light, and the like.

Source: Webster’s Unabridged Dictionary 1913 Edition