Emily Dickinson Lexicon

SOUND, n.² [Sax. sund, a narrow sea or strait, a swimming; Sw. and Dan. sund; Pers. شَنَا shana, a swimming, L. natatio. Qu. can this name be given to a narrow sea because wild beasts were accustomed to pass it by swimming, like Bosporus; or is the word from the root of sound, whole, denoting a stretch, or narrowness, from stretching, like straight; or, from its sounding?]

A narrow passage of water, or a strait between the main land and an isle; or a strait connecting two seas, or connecting a sea or lake with the ocean; as, the sound, which connects the Baltic with the ocean, between Denmark and Sweden; the sound that separates Long Island from the main land of New York and Connecticut.