late 14c., abaishen, from Old French abaissier "diminish, make lower in value or status" (12c.), from Vulgar Latin *ad bassiare "bring lower," from Late Latin bassus "thick, fat, low;" from the same source as base (adj.) and altered 16c. in English by influence of it, which made it an exception to the rule that Old French verbs with stem -iss- enter English as -ish. Related: Abased; abasing.