re·flux / ˈrēˌfləks/ • n. Chem. the process of boiling a liquid in such a way that any vapor is liquefied and returned to the stock. ∎ technical the flowing back of a liquid, esp. that of a fluid in the body.• v. [intr.] Chem. boil or cause to boil in circumstances such that the vapor returns to the stock of liquid after condensing. ∎ [intr.] technical (of a liquid, esp. a bodily fluid) flow back.