thiazidePronunciation: /ˈθʌɪəzʌɪd/Definition of thiazide noun Medicine any of a class of sulphur-containing drugs that increase the excretion of sodium and chloride and are used as diuretics and to assist in lowering the blood pressure: [as modifier]:thiazide diureticsOrigin: 1950s: from elements of thio- + azine + oxidethiazide in other Oxford dictionaries Definition of thiazide in the US English dictionary