accidental
adventitious, casual, chance, contingent, fortuitous, haphazard, inadvertent, incidental, inessential, nonessential, random, uncalculated, uncertain, unessential, unexpected, unforeseen, unintended, unintentional, unlooked-for, unplanned, unpremeditated, unwitting, calculated, designed, expected, foreseen, intended, intentional, planned, prepared