c. 1300, "not filled, held, or occupied," from Old French vacant "idle, unoccupied" (of an office, etc.), from Latin vacantem (nominative vacans), "empty, unoccupied," present participle of vacare "be empty," from PIE *wak-, extended form of root *eue- "to leave, abandon, give out." Meaning "characterized by absence of mental occupation" is from 1570s. Related: Vacantly.