fanny vs female genital organ

fanny and female genital organ both are nouns.

Word	Noun	Adjective	Verb	Adverb
fanny	Yes	No	No	No
female genital organ	Yes	No	No	No

As nouns, fanny and female genital organ are synonyms defined as:

Other synonyms of fanny include female genitalia, female genitals.

fanny (noun)	female genital organ (noun)
the fleshy part of the human body that you sit on	external female sex organs
external female sex organs