As a noun, sound is what you hear when something vibrates and sends waves through air or another material. As a verb, it means to make a noise or to seem in a certain way when heard. As an adjective, it can mean healthy, safe, or reliable.
Noun/verb *sound* (noise) comes from Old English *sund* or *sond*, related to Latin *sonus* “sound.” Adjective *sound* (healthy, solid) is from a different Old English root *gesund* “healthy,” related to *soundness* and German *gesund*.
English hides two different words inside *sound*: one about noise and one about health and strength. That’s why you can have a “sound mind in a sound body” and also “the sound of music”—same spelling, totally different family trees.
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