fellow vs lover

fellow and lover both are nouns.

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

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

Other hypernyms of fellow include adult male, man.

fellow (noun)	lover (noun)
a boy or man	a person who loves someone or is loved by someone
a man who is the lover of a man or woman	an ardent follower and admirer
a friend who is frequently in the company of another	a significant other to whom you are not related by marriage
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