Source : Webster's Revised Unabridged Dictionary (1913)

Impotence \Im"po*tence\, Impotency \Im"po*ten*cy\, n. [L.
   impotenia inability, poverty, want of moderation. See
   {Impotent}.]
   1. The quality or condition of being impotent; want of
      strength or power, animal, intellectual, or moral;
      weakness; feebleness; inability; imbecility.

            Some were poor by impotency of nature; as young
            fatherless children, old decrepit persons, idiots,
            and cripples.                         --Hayward.

            O, impotence of mind in body strong!  --Milton.

   2. Want of self-restraint or self-control. [R.] --Milton.

   3. (Law & Med.) Want of procreative power; inability to
      copulate, or beget children; also, sometimes, sterility;
      barrenness.

Source : WordNet®

impotency
     n 1: the quality of lacking strength or power; being weak and
          feeble [syn: {powerlessness}, {impotence}] [ant: {power},
           {power}]
     2: an inability (usually of a male) to copulate [syn: {impotence}]