party girl vs missy

party girl and missy both are nouns.

Word	Noun	Adjective	Verb	Adverb
party girl	Yes	No	No	No
missy	Yes	No	No	No

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

party girl: an attractive young woman hired to attend parties and entertain men
missy: a young female

Other hypernyms of party girl include fille, girl, miss, young lady, young woman.

party girl (noun)	missy (noun)
an attractive young woman hired to attend parties and entertain men	a young female