/ ˌaɪsəʊˈtɒnɪk; NAmE ˌaɪsoʊˈtɑːn-/ adjective
( of a drink ) with added minerals and salts, intended to replace those lost during exercise
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WORD ORIGIN
early 19th cent. (as a musical term designating a system of tuning, characterized by equal intervals): from Greek isotonos , from isos equal + tonos tone.