1. (a.) Of or pertaining to an occasion or to occasions; occurring at times, but not constant, regular, or systematic; made or happening as opportunity requires or admits; casual; incidental; as, occasional remarks, or efforts.

2. (a.) Produced by accident; as, the occasional origin of a thing.

accessory accidental accompanying additional ado adventitious afloat afoot aleatory auxiliary behind the scenes by-the-way casual causal causative ceremonial circumstantial conditional constitutive contingent current decisive determinative doing effectual etiological eventuating extra few formative going on happening in hand in the wind incidental inessential infrequent institutive intermittent irregular nonessential occurring odd off on on foot ongoing originative out-of-the-way parenthetical part-time particular passing periodic pivotal prevailing prevalent provisional random rare resultant ritual scarce seldom side spare special sporadic supplementary taking place uncommon under way unessential unfrequent