emeritus (adj.)

"having served out one's time, having done sufficient service," c. 1600, from Latin emeritus "veteran soldier who has served his time," noun use of adjective meaning literally "that has finished work, past service," past participle of emerere "serve out, complete one's service," from assimilated form of ex "out" (see ex-) + merere "to serve, earn," from PIE root *(s)mer- (2) "to get a share of something." First used of retired professors 1794 in American English.