IMPEN'ETRABLE, adjective [Latin impenetrabilis; in and penetrabilis, from penetro, to penetrate.] 1. That cannot be penetrated or pierced; not admitting the passage of other bodies; as an impenetrable shield. 2. Not to be affected or moved; not admitting impressions on the mind. The hardened sinner remains impenetrable to the admonitions of the gospel. 3. Not to be entered by the sight; as impenetrable darkness. Hence, 4. Not to be entered and viewed by the eye of the intellect; as impenetrable obscurity or abstruseness.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI