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

1) mishap, misfortune, mischance, misadventure, blunder, mistake; casualty, disaster, catastrophe, calamity: A high percentage of the road accidents were caused by drunken drivers. 2) chance, fortune, luck, fortuity, fluke; serendipity: I came across the gold ring by accident, when cleaning out a disused cupboard. 3) non-essential, accessory or accessary, extra, addition: Melancholy is an almost inseparable accident of old age.