flue (n.)youdaoicibaDictYouDict[flue 词源字典]
"smoke channel in a chimney," 1580s, of uncertain origin, perhaps related to Middle English flue, flewe "mouthpiece of a hunting horn" (early 15c.), which is perhaps from Old French fluie "stream;" or the modern word is perhaps from Old English flowan "to flow." Originally a small chimney in a furnace connected to the main chimney.[flue etymology, flue origin, 英语词源]