party favour vs souvenir

party favour and souvenir both are nouns.

Word	Noun	Adjective	Verb	Adverb
party favour	Yes	No	No	No
souvenir	Yes	No	No	No

As nouns, souvenir is a hypernym of party favour; that is, souvenir is a word with a broader meaning than party favour:

party favour: souvenir consisting of a small gift given to a guest at a party
souvenir: something of sentimental value

Other hypernyms of party favour include keepsake, relic, token.

party favour (noun)	souvenir (noun)
souvenir consisting of a small gift given to a guest at a party	something of sentimental value
	a reminder of past events