co-worker vs colleague

co-worker and colleague both are nouns.

Word	Noun	Adjective	Verb	Adverb
co-worker	Yes	No	No	No
colleague	Yes	No	No	No

As nouns, co-worker and colleague are synonyms defined as:

Other synonyms of co-worker include fellow worker, workfellow.

co-worker (noun)	colleague (noun)
an associate that one works with	an associate that one works with
	a person who is member of one's class or profession