That which has the property of inducing quiet or calm, as a sedative medicine.(noun)
The Century Dictionary (Public Domain)
Use "quietive" in a sentence
"For every sort of pleasure is never anything more than the quietive of some need or longing; and that pleasure should come to an end as soon as the need ceases, is no more a subject of complaint than that a man cannot go on eating after he has had his dinner, or fall asleep again after a good night’s rest."