"animal doctor, one who practices the art of treating disease and injuries in domestic animals," 1640s, from Latin veterinarius "of or having to do with beasts of burden," also, as a noun, "cattle doctor," from veterinum "beast of burden," perhaps from vetus (genitive veteris) "old" (see veteran), possibly from the notion of "experienced," or of "one year old" (hence strong enough to draw burdens). Another theory connects it to Latin vehere "to draw," on notion of "used as a draft animal." Replaced native dog-leech (1520s).
"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.