by 1831, from French calmatif; see calm (adj.) + -ative. A hybrid word; purists prefer sedative. "The Latinic suffix is here defensible on the ground of It. and Sp. calmar, F. calmer ...." [OED].
calmative calm·a·tive (kä'mə-tĭv, kāl'mə-)adj. Having relaxing or pacifying properties. n. A sedative.