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Example:The boom of the thunder startled the horses.

Definition:a deep, loud, resonant sound, typically produced by a sudden release of energy or by a large and heavy object striking against another and making a very loud sound.

Example:The drone of the jet engines filled the sky.

Definition:a long, continuous, and monotonous sound, especially the low-pitched sound produced by an engine or machine.

Example:She could feel her heartbeat, steady and strong.

Definition:a regular, often soothing sound, especially as produced by the beating of a person’s heart.