souvenir vs party favor

souvenir and party favor both are nouns.

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

As nouns, party favor is a hyponym of souvenir; that is, party favor is a word with a more specific, narrower meaning than souvenir:

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

Other hyponyms of souvenir include love-token, favor, favour, party favour.

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