pet vs beast

pet and beast both are nouns.

Word	Noun	Adjective	Verb	Adverb
pet	Yes	Yes	Yes	No
beast	Yes	No	No	No

As nouns, beast is a hypernym of pet; that is, beast is a word with a broader meaning than pet:

Other hypernyms of pet include animal, animate being, brute, creature, fauna.

pet (noun)	beast (noun)
a domesticated animal kept for companionship or amusement	a living organism characterized by voluntary movement
a fit of petulance or sulkiness (especially at what is felt to be a slight)	a cruelly rapacious person
a special loved one

pet (adjective)	beast (adjective)
preferred above all others and treated with partiality

pet (verb)	beast (verb)
stroke or caress gently
stroke or caress in an erotic manner, as during lovemaking