companion vs playfellow

companion and playfellow both are nouns.

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

As nouns, playfellow is a hyponym of companion; that is, playfellow is a word with a more specific, narrower meaning than companion:

Other hyponyms of companion include date, escort, playmate, tovarich, tovarisch.

companion (noun)	playfellow (noun)
a friend who is frequently in the company of another	a companion at play
one paid to accompany or assist or live with another
a traveler who accompanies you

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