Douglas Harper's Etymology Dictionary
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].
Wiktionary
a. That calms n. A drug with calming effects.
Usage examples of "calmative".
Lesh had dispatched two of her assistants to find fruit and funqi from which nourishing juices could be extracted, at a safe distance from the lake, and herself administered a calmative from the first-aid pack she had brought.
Ugant, however, was affability itself as the beast swung into the interlocking tree-crowns and headed east, adroitly dodging other traffic without further orders, and her small talk was calmative, at least.
He was in no emotional state to fill an active role in the metaconcert so he was given a deep course of calmative redaction that almost completely cut off his volition.
His vital-signs display showed compensatory oxygenation kicking in, together with a flow of calmative redaction.
The current situation had him gulping handfuls of calmatives on a daily basis.