IMPER'VIOUS, adjective [Latin impervius; in and pervius, passable; per and via, way.] 1. Not to be penetrated or passed through; impenetrable; as an impervious gulf; an impervious forest. 2. Not penetrable; not to be pierced by a pointed instrument; as an impervious shield. 3. Not penetrable by light; not permeable to fluids. Glass is pervious to light, but impervious to water. Paper is impervious to light. In the latter sense only, impervious is synonymous with impermeable.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI