To sound. 1. To measure the depth of; to fathom; especially, to ascertain the depth of by means of a line and plummet. 2. To ascertain the depth of water with a sounding line or other device. 3. To make a noise; to utter a voice; to make an impulse of the air that shall strike the organs of hearing with a perceptible effect. 4. To causse to make a noise; to play on; as, to sound a trumpet or a horn.