colleague vs co-worker

colleague and co-worker both are nouns.

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

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

Other synonyms of colleague include fellow worker, workfellow.

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