Wiktionary
reflux condenser
n. (context chemistry English) A water-cooled, double walled piece of laboratory glassware that is fitted on top of a vessel of boiling liquid such that vapour condenses and flows back into the vessel, preventing the contents from boiling dry.
WordNet
reflux condenser
n. condenser such that vapor over a boiling liquid is condensed and flows back into the vessel to prevent its contents from boiling dry