incidentyoudaoicibaDictYouDict[incident 词源字典]
incident: [15] An incident is literally that which ‘befalls’. In common with accident and occident, and a wide range of other English words, from cadaver to occasion, it comes ultimately from Latin cadere ‘fall’. This was combined with the prefix in- ‘on’ to produce incidere ‘fall on’, hence ‘befall, happen to’. Its present participial stem incident- passed into English either directly or via French.

The use of a word that literally means ‘fall’ to denote the concept of ‘happening’ is quite a common phenomenon. It occurs also in befall and chance, and operates in other languages than English; Welsh digwydd ‘happen’, for instance, is derived from cwyddo ‘fall’.
=> accident, cadence, case, occasion[incident etymology, incident origin, 英语词源]
incident (n.)youdaoicibaDictYouDict
early 15c., "something which occurs casually in connection with something else," from Middle French incident and directly from Latin incidentem (nominative incidens), present participle of incidere "happen, befall," from in- "on" + -cidere, comb. form of cadere "to fall" (see case (n.1)). Sense of "an occurrence viewed as a separate circumstance" is from mid-15c. Meaning "event that might trigger a crisis or political unrest" first attested 1913.
incident (adj.)youdaoicibaDictYouDict
"conducive (to), contributing (to)," early 15c., from Middle French incident (adj.) or directly from Latin incidens, present participle of incidere (see incident (n.)).