late 14c., from O.Fr. tranquilite
(12c.), from L. tranquillitatem
) "tranquilness," from tranquillus
"tranquil," perhaps from trans-
"over" (here in sense of "exceedingly") + a root related to quies
"rest" (see quiet
formed in Eng. 1620s; tranquilizer
"sedative" is from 1824 (first reference is to ground ivy); in reference to one of a large group of anti-anxiety drugs, it is first recorded 1956.