veteran (n.)

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.

Definitions of veteran
veteran (n.)
a serviceman who has seen considerable active service;
the veterans laughed at the new recruits
Synonyms: veteran soldier
veteran (n.)
a person who has served in the armed forces;
Synonyms: vet / ex-serviceman
veteran (n.)
an experienced person who has been through many battles; someone who has given long service;
Synonyms: old-timer / oldtimer / old hand / warhorse / old stager / stager
veteran (adj.)
rendered competent through trial and experience;
veteran steadiness
a veteran officer
Synonyms: seasoned