Top Definition
Isotonic is a popular recently developed type of sports drink, usually with Glucose or Fructose flavouring. Its mostly known as a cheap alternative to branded sports drinks such as 'Lucozade' or 'Powerade'.
"Hey look they have powerade" "Nah, I think ill go with some cheap Isotonic"
by PurpleRubberDuckie June 09, 2009

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