n. 25B6; noun
she wore a mask to conceal her face : DISGUISE, false face; historical domino, visor; archaic vizard.
he dropped his mask of good humour : PRETENCE, semblance, veil, screen, front, false front, facade, veneer, blind, false colours, disguise, guise, concealment, cover, cover-up, cloak, camouflage.
25B6; verb poplar trees masked the factory : HIDE, conceal, disguise, cover up, obscure, screen, cloak, camouflage, veil.