Source : Webster's Revised Unabridged Dictionary (1913)

Impuissance \Im*pu"is*sance\, n. [Cf. F. impuissance.]
   Lack of power; inability. --Bacon.

         Their own impuissance and weakness.      --Holland.

Source : WordNet®

impuissance
     n : powerlessness revealed by an inability to act; "in spite of
         their weakness the group remains highly active" [syn: {helplessness},
          {weakness}]