Origin of fortuitous
Many object to the use of fortuitous to mean simply “fortunate” and insist that it should be limited to its original sense of “accidental.” In modern standard use, however, fortuitous almost always carries the senses both of accident or chance and luck or fortune. It is infrequently used in its sense of “accidental” without the suggestion of good luck, and even less frequently in the sense “lucky” without at least a suggestion of accident or chance: A fortuitous encounter with a former schoolmate led to a new and successful career for the artist.
British Dictionary definitions for unfortuitous
Word Origin for fortuitous
Word Origin and History for unfortuitous
1650s, from Latin fortuitus "happening by chance, casual, accidental," from forte "by chance," ablative of fors "chance" (related to fortuna; see fortune). It means "accidental, undesigned" not "fortunate." Earlier in this sense was fortuit (late 14c.), from French. Related: Fortuitously; fortuitousness.