lacking physical strength or vigor; weak / lacking in power, as to act effectively; helpless

a man who has erectile dysfunction / an impotent or powerless person

In an impotent manner.

plural of impotent

Powerlessness; incapacity. / Inability to copulate or beget children; sterility, erectile dysfunction, etc.

(dated) impotence

(rare) not drinkable

plural of impotence

plural of impotency

(botany) Incapable of self-fertilization.