girl vs missy

girl and missy both are nouns.

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

As nouns, girl and missy are synonyms defined as:

Other synonyms of girl include fille, miss, young lady, young woman.

girl (noun)	missy (noun)
a young female	a young female
a girl or young woman with whom a man is romantically involved
a youthful female person
a friendly informal reference to a grown woman
a female human offspring