INEXPUGNABLE
impregnable, inexpugnable
(adjective) incapable of being overcome, challenged or refuted; “an impregnable argument”; “impregnable self-confidence”
Source: WordNet® 3.1
Etymology
Adjective
inexpugnable (comparative more inexpugnable, superlative most inexpugnable)
Impossible to eliminate or destroy; impregnable.
Anagrams
• inexpungable
Source: Wiktionary
In`ex*pug"na*ble, a. Etym: [L. inexpugnabilis: cf. F. inexpugnable.
See In- not, and Expugnable.]
Definition: Incapable of being subdued by force; impregnable;
unconquerable. Burke.
A fortress, inexpugnable by the arts of war. Milman.
Source: Webster’s Unabridged Dictionary 1913 Edition