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," from Old Latin pro spere "according to expectation," from pro "for" + ablative of spes "hope," from PIE root *spe- "to flourish, succeed, thrive, prosper" (see speed (n.)).