simian adj.

c. 1600, in reference to human features or qualities, "characteristic of or resembling monkeys or apes," with -ian + Latin simia "ape," from simus "snub-nosed," from Greek simos "snub-nosed" (like the Scythians), also a masculine proper name, a word of unknown origin.

In 18c. and for a time after Latin Simia was taken as the genus name of the primates, hence the biological meaning "pertaining to monkeys" (by 1863). The noun meaning "an ape or monkey" is attested from 1880.