fellow vs companion

fellow and companion both are nouns.

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

As nouns, fellow and companion are synonyms defined as:

fellow and companion: a friend who is frequently in the company of another

Other synonyms of fellow include associate, comrade, familiar.

fellow (noun)	companion (noun)
a boy or man	a friend who is frequently in the company of another
a man who is the lover of a man or woman	one paid to accompany or assist or live with another
a friend who is frequently in the company of another	a traveler who accompanies you
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

fellow (verb)	companion (verb)
	be a companion to somebody