online medical dictionary | definition of impenetrable

1. Incapable of being penetrated or pierced; not admitting the passage of other bodies; not to be entered; impervious; as, an impenetrable shield. "Highest woods impenetrable To star or sunlight." (Milton)

2. <physics> Having the property of preventing any other substance from occupying the same space at the same time.

3. Inaccessible, as to knowledge, reason, sympathy, etc.; unimpressible; not to be moved by arguments or motives; as, an impenetrable mind, or heart. "They will be credulous in all affairs of life, but impenetrable by a sermon of the gospel." (Jer. Taylor)

Origin: L. Impenetrabilis; pref. Im- not + penetrabilis penetrable: cf. F. Impenetrable.

(01 Mar 1998)