favourite vs pet

favourite and pet both are nouns.

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

As adjectives, favourite and pet are synonyms defined as:

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

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

As nouns, favourite and pet are synonyms defined as:

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

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

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

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