Not to be penetrated or passed through; impenetrable; as an impervious gulf; an impervious forest.

Not penetrable; not to be pierced by a pointed instrument; as an impervious shield.

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.