incidence

noun

Etymology: From Middle French incidence, from Medieval Latin incidentia (“a falling upon”), from Latin incidens, present participle of incidere (“to fall upon”), from in (“on”) + cadere (“to fall”).

1. The act of something happening; occurrence.
2. The extent or the relative frequency of something happening.
3. The manner of falling; bearing or onus, as of a tax that falls unequally.
4. The striking of radiation or a projectile upon a surface.
5. A measure of the rate of new occurrence of a given medical condition in a population within a specified period of time.
6. The falling of a point on a line, or a line on a plane.
7. The relation between an edge of a graph and one of the vertices it connects.