ring girl vs missy

ring girl and missy both are nouns.

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

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

ring girl: a young woman who holds up cards indicating the number of the next round at prize fights
missy: a young female

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

ring girl (noun)	missy (noun)
a young woman who holds up cards indicating the number of the next round at prize fights	a young female