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. By some, religious duties . . . appear to be regarded . . . as an incidental business. Rogers.
Syn. -- Accidental; casual; fortuitous; contingent; chance; collateral. See Accidental. -- In`cen*den"tal*ly, adv. -- In`cen*den"tal*ness, n. I treat either or incidentally of colors. Boyle.
1 other Webster entry under this spelling
Incidental, n.
An incident; that which is incidental; esp., in the plural, an aggregate of subordinate or incidental items not particularized; as, the expense of tuition and incidentals. Pope.
Shades of meaning
Fernald lists incidental only as an antonym, under inherent.
He lists it without comment; the entries above explain its neighbors.