n.1 a smoke-duct in a chimney.
2 a channel for conveying heat, esp. a hot-air passage in a wall; a tube for heating water in some kinds of boiler.
Phrases and idioms:
flue-cure cure (tobacco) by artificial heat from flues. flue-pipe an organ pipe into which the air enters directly, not striking a reed.
Etymology: 16th c.: orig. unkn.