Unable to be affected by or penetrated by something; completely resistant to influence or damage.
From Latin impervia, composed of in- (not) and pervius (having a way through), from per- (through) and via (way). The word entered English in the 17th century, initially used for physical barriers before extending to emotional or intellectual resistance.
Interestingly, materials that are impervious to water might be pervious to air, showing that imperviousness is always relative to what's trying to pass through. In psychology, being impervious to criticism can be both a strength and a weakness, protecting self-esteem while potentially blocking valuable feedback.
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