IMPREG'NABLE, adjective 1. Not to be stormed, or taken by assault; that cannot be reduced by force; able to resist attack; as an impregnable fortress. 2. Not to be moved, impressed or shaken; invincible. The man's affection remains wholly unconcerned and impregnable
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI