INVULNERABLE
invulnerable
(adjective) immune to attack; impregnable; “gunners raked the beach from invulnerable positions on the cliffs”
Source: WordNet® 3.1
Etymology
Adjective
invulnerable (not comparable)
Incapable of being injured; not vulnerable.
Unanswerable; irrefutable
Source: Wiktionary
In*vul"ner*a*ble, a. Etym: [L. invulnerabilis: cf. F. invulnérable.
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: Webster’s Unabridged Dictionary 1913 Edition