depressant (n.)

late 14c., "put down by force, conquer," a sense now obsolete, from Old French depresser "to press down, lower," from Late Latin depressare, frequentative of Latin deprimere "press down," from de "down" (see de-) + premere "to press, hold fast, cover, crowd, compress" (from PIE root *per- (4) "to strike").

Meaning "push down physically, press or move downward" is from early 15c.; that of "deject, make gloomy, lower in feeling" is from 1620s; economic sense of "lower in value" is from 1878.

agent or instrumental suffix, from Old French and French -ant, from Latin -antem, accusative of -ans, present-participle suffix of many Latin verbs. Compare -ance.

"chemical used to treat symptoms of depression," 1876, from anti- + depressant.