girl vs flapper

girl and flapper both are nouns.

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

As nouns, flapper is a hyponym of girl; that is, flapper is a word with a more specific, narrower meaning than girl:

girl: a young female
flapper: a young woman in the 1920s who flaunted her unconventional conduct and dress

girl (noun)	flapper (noun)
a young female	a young woman in the 1920s who flaunted her unconventional conduct and dress
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