Merriam-Webster Collegiate Dictionary - incident

 I. noun  Etymology: Middle English, from Middle French, from Medieval Latin ~-, incidens, from Latin, present participle of incidere to fall into, from in- + cadere to fall — more at chance  Date: 15th century  1. something dependent on or subordinate to something else of greater or principal importance  2.  a. an occurrence of an action or situation that is a separate unit of experience ; happening  b. an accompanying minor occurrence or condition ; concomitant  3. an action likely to lead to grave consequences especially in diplomatic matters a serious border ~  Synonyms: see occurrence  II. adjective  Date: 15th century  1. occurring or likely to occur especially as a minor consequence or accompaniment the confusion ~ to moving day  2. dependent on or relating to another thing in law  3. falling or striking on something ~ light rays