Source : Webster's Revised Unabridged Dictionary (1913)

Puissance \Pu"is*sance\, n. [F., fr. puissant. See {Puissant},
   and cf. {Potency}, {Potance}, {Potence}.]
   Power; strength; might; force; potency. `` Youths of
   puissance.'' --Tennyson.

         The power and puissance of the king.     --Shak.

   Note: In Spenser, Shakespeare, and Milton, puissance and
         puissant are usually dissyllables.

Source : WordNet®

puissance
     n : power to influence or coerce; "the puissance of the labor
         vote"