Webster's Revised Unabridged Dictionary · 1913

Puissance

Puissance , noun

[French, from puissant. See Puissant, and compare Potency, Potance, Potence.]

Power; strength; might; force; potency.
Youths of puissance. — Tennyson
The power and puissance of the king. — Shakespeare

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