Incidental means happening as a minor side effect of something else. Incidental costs, incidental damage, incidental music.
It marks something as a by-product rather than the point, which is why incidental expenses are the small ones nobody planned for. Incidental music is written to accompany a play rather than to stand alone. Note incidentally, which as a sentence adverb means by the way.
1adjectiveincidentalHappening as a minor side effect of something else.
“The road was built for trade, but an incidental benefit was less traffic in the old town.”
incidental is a quality of being a side effect.
Proto-Indo-European
*ḱh₂d-
Latin
incidens
Middle French
incident
English
incident
English, today
incidental
Built from
From incident + -al. incident Recorded since 1412, from Middle French incident, from Latin incidens, the present active participle of incidō (“to happen, befall”), itself from in- (“on”) + -cidō, the combining form of cadō (“to fall”).
Etymology from Wiktionary, CC BY-SA