impotency vs ED

impotency and ED both are nouns.

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

As nouns, ED is a hyponym of impotency; that is, ED is a word with a more specific, narrower meaning than impotency:

impotency: an inability (usually of the male animal) to copulate
ED: impotence resulting from a man's inability to have or maintain an erection of his penis

Other hyponyms of impotency include erectile dysfunction, male erecticle dysfunction.

impotency (noun)	ED (noun)
the quality of lacking strength or power; being weak and feeble	impotence resulting from a man's inability to have or maintain an erection of his penis
an inability (usually of the male animal) to copulate