pet vs favourite

pet and favourite both are nouns.

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

As adjectives, pet and favourite are synonyms defined as:

pet and favourite: preferred above all others and treated with partiality

Other synonyms of pet include best-loved, favored, favorite, favoured, preferent, preferred.

As nouns, pet and favourite are synonyms defined as:

Other synonyms of pet include darling, dearie, deary, ducky, favorite.

pet (noun)	favourite (noun)
a domesticated animal kept for companionship or amusement	something regarded with special favor or liking
a fit of petulance or sulkiness (especially at what is felt to be a slight)	a special loved one
a special loved one	a competitor thought likely to win

pet (adjective)	favourite (adjective)
preferred above all others and treated with partiality	preferred above all others and treated with partiality
	appealing to the general public

pet (verb)	favourite (verb)
stroke or caress gently	To mark an item as a personal favorite on social media
stroke or caress in an erotic manner, as during lovemaking