Source : Webster's Revised Unabridged Dictionary (1913)

Invincibility \In*vin`ci*bil"i*ty\, n. [Cf. F.
   invincibilit['e].]
   The quality or state of being invincible; invincibleness.

Source : WordNet®

invincibility
     n : the property being difficult or impossible to defeat [syn: {indomitability}]