Incidental (?), a. Happening, as an occasional event, without regularity; coming without design; casual; accidental; hence, not of prime concern; subordinate; collateral; as, an incidental conversation; an incidental occurrence; incidental expenses.
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By some, religious duties . . . appear to be regarded . . . as an incidental business. Rogers.

Syn. -- Accidental; casual; fortuitous; contingent; chance; collateral. See Accidental.

-- In`ci*den"tal*ly, adv. -- In`ci*den"tal*ness, n.
[1913 Webster]

I treat either or incidentally of colors. Boyle.
[1913 Webster]