a distinct piece of action, or an episode, as in a story or play.
3.
something that occurs casually in connection with something else.
4.
something appertaining or attaching to something else.
5.
an occurrence of seemingly minor importance, especially involving nations or factions between which relations are strained and sensitive, that can lead to serious consequences, as an outbreak of hostilities or a war: border incident; international incident.
Origin: 1375–1425; late Middle English < Middle French < Medieval Latin incident- (stem of incidēns a happening, noun use of present participle of Latin incidere to befall), equivalent to Latin in-in-2 + -cid- (combining form of cad- fall) + -ent--ent; compare cadence
1412, "something which occurs casually in connection with something else," from L. incidentem (nom. incidens), prp. of incidere "happen, befall," from in- "on" + -cidere, comb. form of cadere "to fall" (see case (1)). Sense of "an occurrence viewed as a separate circumstance"
is from 1462. Meaning "event that might trigger a crisis or political unrest" first attested 1913. Incidental "casual, occasional" first recorded in Milton (1644). Conversational use of incidentally for "by the way" first attested 1925.