colleague vs fellow

colleague and fellow both are nouns.

Word	Noun	Adjective	Verb	Adverb
colleague	Yes	No	No	No
fellow	Yes	No	No	No

As nouns, colleague and fellow are synonyms defined as:

colleague and fellow: a person who is member of one's class or profession

Other synonyms of colleague include confrere.

colleague (noun)	fellow (noun)
an associate that one works with	a boy or man
a person who is member of one's class or profession	a man who is the lover of a man or woman
	a friend who is frequently in the company of another
	a person who is member of one's class or profession
	an informal form of address for a man
	a member of a learned society
	one of a pair