impregnable vs inexpugnable

impregnable and inexpugnable both are adjectives.

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

As adjectives, impregnable and inexpugnable are synonyms defined as:

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

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