old-timer vs veteran

old-timer and veteran both are nouns.

Word	Noun	Adjective	Verb	Adverb
old-timer	Yes	No	No	No
veteran	Yes	Yes	No	No

As nouns, old-timer and veteran are synonyms defined as:

old-timer and veteran: an experienced person who has been through many battles; someone who has given long service

Other synonyms of old-timer include old hand, old stager, oldtimer, stager, warhorse.

old-timer (noun)	veteran (noun)
an elderly man	an experienced person who has been through many battles; someone who has given long service
an experienced person who has been through many battles; someone who has given long service	a person who has served in the armed forces
	a serviceman who has seen considerable active service

old-timer (adjective)	veteran (adjective)
	rendered competent through trial and experience