unattackable vs impregnable

unattackable and impregnable both are adjectives.

Word	Noun	Adjective	Verb	Adverb
unattackable	No	Yes	No	No
impregnable	No	Yes	No	No

As adjectives, unattackable and impregnable are synonyms defined as:

unattackable and impregnable: immune to attack; incapable of being tampered with

Other synonyms of unattackable include inviolable, secure, strong, unassailable.

unattackable (adjective)	impregnable (adjective)
immune to attack; incapable of being tampered with	capable of conceiving
	immune to attack; incapable of being tampered with
	incapable of being overcome, challenged or refuted