1.Definition: (sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence

"Incidental expenses", "The road will bring other incidental advantages", "Extra duties incidental to the job", "Labor problems incidental to a rapid expansion", "Confusion incidental to a quick change"

Related Adjective(s):incidental

2.Definition: falling or striking of light rays on something

"Incident light"