impotence vs impotency

impotence and impotency both are nouns.

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

As nouns, impotence and impotency are synonyms defined as:

impotence and impotency: the quality of lacking strength or power; being weak and feeble

Other synonyms of impotence include powerlessness.

As nouns, impotence and impotency are synonyms defined as:

impotence and impotency: an inability (usually of the male animal) to copulate

impotence (noun)	impotency (noun)
the quality of lacking strength or power; being weak and feeble	the quality of lacking strength or power; being weak and feeble
an inability (usually of the male animal) to copulate	an inability (usually of the male animal) to copulate