from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The rate or extent of occurrence or effect.
  • noun Usage Problem The fact or an instance of happening; occurrence.
  • noun The arrival of radiation or a projectile at a surface.
  • noun Angle of incidence.

from The Century Dictionary.

  • noun The actual fall of taxation upon a particular individual or piece of property, in distinction from its nominal or supposed distribution.
  • noun A subordinate occurrence or thing; an incident; something incidental or casual.
  • noun The manner of falling; direction of the line of fall; course.
  • noun 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.
  • noun In astronomy, same as immersion, 4.
  • noun 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.
  • noun In gunnery, the angle which the longer axis of a projectile makes with the surface struck.

from the GNU version of the Collaborative International Dictionary of English.

  • noun obsolete A falling on or upon; an incident; an event; an occurrence.
  • noun (Physics) The direction in which a body, or a ray of light or heat, falls on any surface.
  • noun The rate or ratio at which something occurs.
  • noun 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.
  • noun the line in the direction of which a surface is struck by a body, ray of light, and the like.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

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

  • noun the striking of a light beam on a surface
  • noun 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