fluid
n. C / Un. any substance that flows easily, such as a liquid or a gas. In a medical context, it often refers to water or juice you drink to stay healthy.
n. a substance, such as a liquid or gas, that has no fixed shape and yields easily to external pressure. In clinical contexts, it refers to any liquid taken into or excreted by the body.
The doctor told me to drink plenty of fluids.
Mechanics checked the car for leaks to ensure all hydraulic fluids were at the correct levels for safe braking.
The patient's recovery was aided by the careful administration of intravenous fluids to maintain electrolyte balance and prevent dehydration during the acute phase of the illness.
From Middle English fluid, from Latin fluidus (“flowing; fluid”), from Latin fluō (“to flow”), from Proto-Indo-European bʰleh₁- (“to swell; surge; overflow; run”). Akin to Ancient Greek φλύειν (phlúein, “to swell; overflow”). Not related to English flow, which is a native, inherited word from plew-, but is distantly related from English bleat.
Uncountable when referring to the general state of matter; countable when referring to specific types or measured quantities of liquids.