mid-14c., from Old French prosperer (14c.) and directly from Latin prosperare "cause to succeed, render happy," from prosperus "favorable, fortunate, prosperous," perhaps literally "agreeable to one's wishes," traditionally regarded as from Old Latin pro spere "according to expectation, according to one's hope," from pro "for" + ablative of spes "hope," from PIE root *spe- "to flourish, succeed, thrive, prosper" (see speed, n.).