oldtimer vs old-timer

oldtimer and old-timer both are nouns.

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

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

Other synonyms of oldtimer include antique, gaffer, old geezer.

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

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

Other synonyms of oldtimer include old hand, old stager, stager, veteran, warhorse.

oldtimer (noun)	old-timer (noun)
an elderly man	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