vet n.1

"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).

c. 1500, "old experienced soldier," from French vétéran, from Latin veteranus "old, aged, that has been long in use," especially of soldiers; as a plural noun, "old soldiers," from vetus (genitive veteris) "old, aged, advanced in years; of a former time," as a plural noun, vetores, "men of old, forefathers," from PIE *wet-es-, from root *wet- (2) "year" (source also of Sanskrit vatsa- "year," Greek etos "year," Hittite witish "year," Old Church Slavonic vetuchu "old," Old Lithuanian vetušas "old, aged;" and compare wether). Latin vetus also is the ultimate source of Italian vecchio, French vieux, Spanish viejo. General sense of "one who has seen long service in any office or position" is attested from 1590s. The adjective first recorded 1610s.

1918, verbal noun from vet (v.).