inexpugnable vs impregnable

inexpugnable and impregnable both are adjectives.

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

As adjectives, inexpugnable and impregnable are synonyms defined as:

inexpugnable and impregnable: incapable of being overcome, challenged or refuted

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