pet vs lover

pet and lover both are nouns.

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

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

pet (noun)	lover (noun)
a domesticated animal kept for companionship or amusement	a person who loves someone or is loved by someone
a fit of petulance or sulkiness (especially at what is felt to be a slight)	an ardent follower and admirer
a special loved one	a significant other to whom you are not related by marriage

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

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