The term 'impervious to sound' is often used in the context of soundproofing, which is the process of making a room or other enclosed space resistant to the passage of sound. The crossword solution for this term is 'soundproof, ' which is a 10-letter word that describes a material or structure that is designed to block sound from entering or leaving a space. Soundproofing is often used in recording studios, theaters, and other places where sound needs to be contained.