fellow vs friend

fellow and friend both are nouns.

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

As nouns, friend is a hypernym of fellow; that is, friend is a word with a broader meaning than fellow:

fellow (noun)	friend (noun)
a boy or man	a person you know well and regard with affection and trust
a man who is the lover of a man or woman	a person with whom you are acquainted
a friend who is frequently in the company of another	an associate who provides cooperation or assistance
a person who is member of one's class or profession	a person who backs a politician or a team etc.
an informal form of address for a man
a member of a learned society
one of a pair