co-worker vs workfellow

co-worker and workfellow both are nouns.

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

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

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

co-worker (noun)	workfellow (noun)
an associate that one works with	an associate that one works with