playfellow vs companion

playfellow and companion both are nouns.

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

As nouns, companion is a hypernym of playfellow; that is, companion is a word with a broader meaning than playfellow:

Other hypernyms of playfellow include associate, comrade, familiar, fellow.

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

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