sex bomb vs young woman

sex bomb and young woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex bomb	Yes	No	No	No
young woman	Yes	No	No	No

As nouns, young woman is a hypernym of sex bomb; that is, young woman is a word with a broader meaning than sex bomb:

Other hypernyms of sex bomb include fille, girl, miss, missy, young lady.

sex bomb (noun)	young woman (noun)
a young woman who is thought to have sex appeal	a young female