soundproof I. \ˈ ̷ ̷| ̷ ̷\adjective Etymology:sound (III) + proof : impervious to sound < a soundproof room > < a soundproof studio > II. transitive verb Etymology: back-formation from soundproofing : to make soundproof : insulate so as to obstruct the passage of sound < called for soundproofing all floors, ceilings, and partitions >