What does efflux mean?
Efflux is a noun denoting the act or process of flowing out, or the substance that flows out. It appears most often in technical and scientific contexts: biologists speak of the efflux of potassium ions from cells, engineers of the efflux of gases or liquids from a system, and physicians of drug efflux as a mechanism by which cancer cells expel chemotherapy agents. A second, more literary sense survives chiefly in law, where 'with the efflux of time' means simply that time has passed. The word derives from Latin fluere, 'to flow', via effluere, 'to flow out', making it a sibling of words like fluent, fluid, and influence. Formal rather than colloquial, efflux lends precision and gravity to descriptions of anything moving outward — a useful alternative to plainer terms like outflow when exactness or elevation of tone matters.
The action or process of flowing out, or the matter that has flowed out; an outflow or discharge.
"The dye traced the efflux of wastewater from the pipe into the river."
Especially common in scientific and medical writing about fluids, gases, or ions leaving a cell or system.
The passage or lapse of time.
"With the efflux of time, the contract's obligations lapsed automatically."
Now confined almost entirely to formal legal language, in phrases such as 'with the efflux of time'.
Rarely pluralized; the word usually appears in the singular even when describing multiple flows.
"The study compared the effluxes of several solutes across the membrane."
Lawyers still say 'with the efflux of time' to mean 'as time passed' — a phrase that has flowed straight down from Latin into modern courtrooms.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of efflux
Efflux comes from Latin effluere, meaning 'to flow out', formed from ex- ('out') plus fluere ('to flow'), the same prolific root behind fluent, fluid, influence, and fluctuate. English adopted the word around the early seventeenth century, initially covering both physical outflows and the passing of time. Its scientific sense remains current today, particularly in physiology and physics.
How efflux is actually used
Formal and technical in register. Common in scientific writing (physics, biology, medicine) for the movement of substances out of cells or systems, and in legal prose for the passage of time. Rare in everyday conversation.
Easily confused with efflux
Afflux means a flow toward a point, whereas efflux means a flow away from or out of it.
Reflux denotes a backward or returning flow, while efflux is simply an outward flow.