from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The act or an instance of happening; occurrence: did not expect criticism and was surprised by its incidence.
  • n. Extent or frequency of occurrence: a high incidence of malaria in the tropics.
  • n. Physics The arrival of radiation or a projectile at a surface.
  • n. Physics Angle of incidence.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The act of something happening; occurrence
  • n. The extent, or the relative frequency of something happening
  • n. The striking of radiation or a projectile upon a surface
  • n. A measure of the risk that a person develops a new condition within a specified period of time, usually a year.

from the GNU version of the Collaborative International Dictionary of English

  • n.
  • n. A falling on or upon; an incident; an event; an occurrence.
  • n. The direction in which a body, or a ray of light or heat, falls on any surface.
  • n. The rate or ratio at which something occurs.

from The Century Dictionary and Cyclopedia

  • n. A subordinate occurrence or thing; an incident; something incidental or casual.
  • n. The manner of falling; direction of the line of fall; course.
  • n. In physics, the falling or impinging of a ray of light or heat, etc., upon a surface: used especially with reference to the direction of the ray.
  • n. In astronomy, same as immersion, 4.
  • n. In geometry, the situation of two figures in which they have something more in common than they would have in some other situation, but do not completely coincide.
  • n. In gunnery, the angle which the longer axis of a projectile makes with the surface struck.
  • n. The actual fall of taxation upon a particular individual or piece of property, in distinction from its nominal or supposed distribution.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the striking of a light beam on a surface
  • n. the relative frequency of occurrence of something


from Wiktionary, Creative Commons Attribution/Share-Alike License

From Medieval Latin incidentia ("a falling upon"), from Latin incidens, present participle of incidere ("to fall upon"), from in ("on") + cadere ("to fall").



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  • I regularly hear people use "incidence" (frequency of occurrence) in place of "incident". They are then forced into "incidences" in place of "incidents".


    "incident" is a occurrence

    "incidence" is how frequently something occurs


    "I was there. I saw the whole incident."

    "The incidence of malapropisms is declining."


    This message has been brought to you by the nerd who read the dictionary when he was a child, and by three cups of his very strong coffee.

    December 29, 2007