what is a definition of sound
sound noun (NOISE). A2 [C or U] something that you can âhear or that can be âheard: They could âhear the sound of a âbell âtolling in the âdistance. She âstood âcompletely still, not making a sound. Suddenly we âheard a âloud âknocking sound from the âengine. Sound can âtravel over very âlarge âdistances in âwater.