'diuretic' originates from Modern Latin/Neo-Latin, specifically the word 'diureticus', ultimately from Greek where the root relates to urination ('diourein'/'diouresis').

'diuretic' passed into English via New Latin/Modern Latin 'diureticus' and French medical usage, derived from Greek elements (related to 'diourein' or 'diuresis') meaning 'to urinate', and became the English term 'diuretic' in the 17th-18th century.

Initially it meant 'causing increased flow or discharge of urine', and over time it has retained that medical meaning as both a noun (a substance) and an adjective (having that effect).