concubine vs fancy woman

concubine and fancy woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
concubine	Yes	No	No	No
fancy woman	Yes	No	No	No

As nouns, fancy woman is a hypernym of concubine; that is, fancy woman is a word with a broader meaning than concubine:

concubine: a woman who cohabits with an important man
fancy woman: an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man

Other hypernyms of concubine include kept woman, mistress.

concubine (noun)	fancy woman (noun)
a woman who cohabits with an important man	an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man
	a woman who engages in sexual intercourse for money