adj. 25B6; adjective
a fortuitous resemblance : CHANCE, adventitious, unexpected, unanticipated, unpredictable, unforeseen, unlooked-for, serendipitous, casual, incidental, coincidental, random, accidental, inadvertent, unintentional, unintended, unplanned, unpremeditated.
United were saved by a fortuitous penalty : LUCKY, fluky, fortunate, providential, advantageous, timely, opportune, serendipitous, heaven-sent; Brit. informal jammy.
predictable, unlucky.