impuissance vs impotency

impuissance and impotency both are nouns.

Word	Noun	Adjective	Verb	Adverb
impuissance	Yes	No	No	No
impotency	Yes	No	No	No

As nouns, impotency is a hypernym of impuissance; that is, impotency is a word with a broader meaning than impuissance:

Other hypernyms of impuissance include impotence, powerlessness.

impuissance (noun)	impotency (noun)
powerlessness revealed by an inability to act	the quality of lacking strength or power; being weak and feeble
	an inability (usually of the male animal) to copulate