The Oxford Thesaurus An A-Z Dictionary of Synonyms - incidentaladj.

1) casual, chance, fortuitous, aleatory, random, haphazard, serendipitous, unpredictable, accidental, adventitious, unplanned, unlooked-for, Colloq fluky: Any good that came from the war was incidental. 2) subordinate, secondary, ancillary, minor, lesser, non-essential, unimportant, trivial, negligible, inconsequential, insignificant, petty, trifling, paltry: The incidental events were not covered by the press.