mid-15c., "unlucky," from un- (1) "not" + fortunate (adj.). Infortunate in same sense is from late 14c. (along with a verb infortune "to render unhappy"). In late 18c.-early 19c., unfortunate woman was a polite way to say "prostitute." The noun meaning "one who is not fortunate" is recorded from 1630s.[unfortunate etymology, unfortunate origin, 英语词源]