[countable, uncountable] (formal or specialist) a liquid; a substance that can flow body fluids (= for example, blood) The doctor told him to drink plenty of fluids. cleaning fluid Word Origin late Middle English (as an adjective): from French fluide or Latin fluidus, from fluere
‘to flow’.Extra examples Change your diet and drink plenty of fluids. It’s important to replace fluids and salts that are lost during exercise. Retaining excess fluid could be a problem. They drained a lot of fluid from his lungs. replacing vital body fluids and salts that are lost when you sweat The attacker’s DNA pattern was identified from a sample of body fluid. The cleaning fluid he was using had been very effective.