impotent

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Lacking physical strength or vigor; weak.
2. adj. Lacking in power, as to act effectively; helpless: "Technology without morality is barbarous; morality without technology is impotent” ( Freeman J. Dyson).
3. adj. Incapable of sexual intercourse, often because of an inability to achieve or sustain an erection.
4. adj. Sterile. Used of males.
5. adj. Obsolete Lacking self-restraint.

Century Dictionary and Cyclopedia

1. Not potent; lacking power, strength, or vigor, physical, intellectual, or moral; powerless; weak; feeble.
2. Wholly lacking in sexual power: said of the male, and rarely of the female.
3. Lacking the power of self-restraint; destitute of self-command; ungovernable.
4. n. One who is feeble, infirm, or languishing under disease.
5. n. A male without sexual power.

Wiktionary

1. adj. Lacking physical strength or vigor; weak.
2. adj. Lacking in power, as to act effectively; helpless.
3. adj. Incapable of sexual intercourse, often because of an inability to achieve or sustain an erection.
4. adj. of a male Sterile.
5. adj. obsolete Lacking self-restraint.

GNU Webster's 1913

1. adj. Not potent; wanting power, strength. or vigor. whether physical, intellectual, or moral; deficient in capacity; destitute of force; weak; feeble; infirm.
2. adj. Wanting the power of self-restraint; incontrolled; ungovernable; violent.
3. adj. (Med.) Wanting the power of procreation; unable to copulate; also, sometimes, sterile; barren. unable to achieve or sustain a penile erection.
4. n. rare One who is impotent.

WordNet 3.0

1. adj. (of a male) unable to copulate
2. adj. lacking power or ability