Source : Webster's Revised Unabridged Dictionary (1913)

Invulnerable \In*vul"ner*a*ble\, a. [L. invulnerabilis: cf. F.
   invuln['e]rable. See {In-} not, and {Vulnerable}.]
   1. Incapable of being wounded, or of receiving injury.

            Neither vainly hope To be invulnerable in those
            bright arms.                          --Milton.

   2. Unanswerable; irrefutable; that can not be refuted or
      convinced; as, an invulnerable argument.

Source : WordNet®

invulnerable
     adj : immune to attack; impregnable; "gunners raked the beach from
           invulnerable positions on the cliffs" [ant: {vulnerable}]