The Collaborative International Dictionary of English v.0.48:

Impotence \Im"po*tence\, Impotency \Im"po*ten*cy\, n. [L.
   impotenia inability, poverty, lack of moderation. See
   Impotent.]
   1. The quality or condition of being impotent; lack of
      strength or power, animal, intellectual, or moral;
      weakness; feebleness; inability; imbecility.
      [1913 Webster]

            Some were poor by impotency of nature; as young
            fatherless children, old decrepit persons, idiots,
            and cripples.                         --Hayward.
      [1913 Webster]

            O, impotence of mind in body strong!  --Milton.
      [1913 Webster]

   2. Lack of self-restraint or self-control. [R.] --Milton.
      [1913 Webster]

   3. (Law & Med.) Lack of procreative power; inability to
      copulate, or beget children; also, sometimes, sterility;
      barrenness; specifically, in males: the inability to
      achieve or sustain a penile erection; erectile
      dysfunction.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "impotence":
   absurdity, adynamia, aimlessness, anemia, aridity, atony,
   barrenness, birth control, blah feeling, bloodlessness,
   bootlessness, cachexia, cachexy, carelessness, carnality, coldness,
   contraception, cowardice, dearth, debilitation, debility, dry womb,
   dryness, dullness, easiness, easygoingness, emptiness, enervation,
   etiolation, faintness, family planning, famine, fatigue, fatuity,
   fecklessness, feebleness, flabbiness, flaccidity, flesh,
   fleshliness, forcelessness, frailty, frigidity, fruitlessness,
   futility, helplessness, hollowness, impotency, imprecision,
   inadequacy, inanity, incompetence, indifference, ineffectiveness,
   ineffectuality, ineffectualness, inefficaciousness, inefficacy,
   ineptness, infecundity, infertility, lack of force,
   lack of influence, lack of magnetism, lack of personality,
   lack of power, languishment, languor, lassitude, laxity, laxness,
   leniency, libido, listlessness, looseness, loosening, love,
   lovemaking, marriage, meaninglessness, negligence, no say,
   nugacity, otiosity, overindulgence, overpermissiveness,
   permissiveness, planned parenthood, pointlessness, potency,
   powerlessness, profitlessness, prostration, purposelessness,
   rat race, relaxation, relaxedness, remissness, sensuality,
   sex drive, sexiness, sexual instinct, sexual urge, sexualism,
   sexuality, slackness, sloppiness, sluggishness, softness,
   sterileness, sterility, strengthlessness, the absurd, triviality,
   unauthoritativeness, unfertileness, unfruitfulness,
   uninfluentiality, unpersuasiveness, unproductiveness,
   unprofitability, unprofitableness, unrestraint, valuelessness,
   vanity, vicious circle, voluptuousness, weakliness, weakness,
   weariness, withered loins, worthlessness



Bouvier's Law Dictionary, Revised 6th Ed (1856):

IMPOTENCE, med. jur. The incapacity for copulation or propagating the
species. It has also been used synonymously with sterility.
     2. Impotence may be considered as incurable, curable, accidental or
temporary. Absolute or incurable impotence, is that for which there is no
known relief, principally originating in some malformation or defect of the
genital organs. Where this defect existed at the time of the marriage, and
was incurable, by the ecclesiastical law and the law of several of the
American states, the marriage may be declared void ab initio. Com. Dig.
Baron and Feme, C 3; Bac. Ab. Marriage, &c., E 3; 1 Bl. Com. 440; Beck's
Med. Jur. 67; Code, lib. 5, t. 17, l. 10; Poyn. on Marr. and Div. ch. 8; 5
Paige, 554; Merl. Rep. mot Impuissance. But it seems the party naturally
impotent cannot allege that fact for the purpose of obtaining a divorce. 3
Phillim. R. 147; S. C. 1 Eng. Eccl. R. 384. See 3 Phillim. R. 325; S. C. 1
Eng. Eccl. R. 408; 1 Chit. Med. Jur. 877; 1 Par. & Fonb. 172, 173. note d;
Ryan's Med. Jur. 95. to 111; 1 Bl. Com. 440; 2 Phillim. R. 10; 1 Hagg. R.
725. See, as to the signs of impotence, 1 Briand, Med. Leg. c. 2, art. 2,
Sec. 2, n. 1; Dictionnaire des Sciences Medicales, art. Impuissance; and,
generally, Trebuchet, Jur. de la. Med. 100, 101, 102; 1 State Tr. 315; 8
State Tr. App. No. 1, p. 23; 3 Phillm. R. 147; 1 Hagg. Eccl. R. 523; Fodere,
Med. Leg. Sec. 237.