impregnably

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im·preg·na·ble 1

I0064900 (ĭm-prĕg′nə-bəl)adj.1. Impossible to capture or enter by force: an impregnable fortress.2. Difficult or impossible to attack, challenge, or refute with success: an impregnable argument.
[Middle English imprenable, from Old French : in-, not (from Latin in-; see in-1) + prenable, pregnauble, pregnable; see pregnable.]
im·preg′na·bly adv.

im·preg·na·ble 2

I0064900 (ĭm-prĕg′nə-bəl)adj. Capable of being impregnated.
[impregn(ate) + -able.]
Thesaurus
Adv.1.impregnably - in an impregnable manner; "the sight of that bland, impregnably righteous face has been enough to make their blood run cold"