(uncountable) Sonic barrier, the sudden increase in drag (resistance) and other effects experienced by moving objects when their speed approaches that of sound or becomes supersonic (which used to be considered a barrier to higher speeds).

(idiomatic) Sleeping still and silently.

(film, television) A soundproof room or building used for the production of movies or of television programmes.

(physics) The longitudinal wave of pressure that is transmitted through any plastic material; audible sound.

(physics) A wave of fluctuating temperature or entropy propagated in the superfluid phase of liquid helium

A thin board that forms part of the resonating chamber of a musical instrument and serves to reinforce its sound / A structure that reflects sound towards the intended listeners

An artificially created or enhanced sound, used to accompany the action of a dramatic production, such as a film, play or video game

(music) A subgenre of country music that became popular in the 1950s and 1960s, containing elements of popular music and characterized by electronic string sections, background vocals, and orchestras.

An acoustic mirror.

plural of sound mirror