Tranquilize \Tran"quil*ize\, Tranquillize \Tran"quil*lize\, v. t. [imp. & p. p. {Tranquilized}or {Tranquilliized}; p. pr. & vb. n. {Tranquilizing}or {Tranquillizing}.] [Cf. F. tranquilliser.] To render tranquil; to allay when agitated; to compose; to make calm and peaceful; as, to tranquilize a state disturbed by factions or civil commotions; to tranquilize the mind. Syn: To quiet; compose; still; soothe; appease; calm; pacify.