Word Origin & History
vainc.1300, "devoid of real value, idle, unprofitable," from O.Fr. vein "worthless," from L. vanus "idle, empty," from PIE *wa-no-, from base *eue- "to leave, abandon, give out" (cf. O.E. wanian "to lessen," wan "deficient;" O.N. vanta "to lack;" L. vacare "to be empty," vastus "empty, waste;" Avestan va-
"lack," Pers. vang "empty, poor;" Skt. una- "deficient"). Meaning "conceited" first recorded 1692, from earlier sense of "silly, idle, foolish" (1390). Phrase in vain "to no effect" (c.1300, after L. in vanum) preserves the original sense.