flue
/flu/noun, adjective
flue is a noun meaning “A pipe or duct that carries gaseous combustion products away from the point of combustion (such as a furnace)” (English Wiktionary, September 2026). It is spelled F-L-U-E and has one syllable, and it appears about once in every 2 million words in written English (wordfreq, 2021 data). The plural of flue is flues.
What does flue mean?
noun
- 1
A pipe or duct that carries gaseous combustion products away from the point of combustion (such as a furnace).
- 2
An enclosed passageway in which to direct a current of air or other gases along.
- 3
obsoleteA woolly or downy substance; down, nap; a piece of this.
- 4
In an organ flue pipe, the opening between the lower lip and the languet.
adjective
- 1
UKAlternative form of flew (“shallow, flat”).
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract).
How do you pronounce flue?
- UK /fluː/
- UK [flʉː]
- US /flu/
Flue has one syllable (counted from its American pronunciation in the CMU Pronouncing Dictionary).
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract). Recordings: LL-Q1860_(eng)-Vealhurl-flue.wav, LL-Q1860_(eng)-عُثمان_(Middle_river_exports)-flue.wav, Wikimedia Commons (author and licence on each file's page).
Forms of flue
- flues plural
- more flue comparative
- most flue superlative
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract).
How common is flue?
Flue appears about once in every 2 million words in written English, the 38,416th most frequent word form in the list.
Source: written frequency: wordfreq 3.1 (a 2021 snapshot of Wikipedia, subtitles, news, books, web text and social media).
Words people confuse with flue
Word pairs people search, with the monthly searches for “a vs b” (G: Google, B: Bing, United States).
Sounds like: flew, flu (Wiktionary's homophone list; some hold only in some accents).
Also written: flew.
Sources: Google and Bing searches (September 2025 to August 2026, through DataForSEO); English Wiktionary (homophones, alternative spellings).
Flue in Spanish, French, German and Portuguese
In the sense pipe that carries gaseous combustion products away from their origin:
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract). Translations are Wiktionary's, by sense; a linked word has its own PlainSpell page.
Where does flue come from?
From Middle English flue, flewe (“mouthpiece of a hunting horn”), of uncertain origin. Perhaps a back-formation from Middle English *flews (mistaken as a plural), from Old English flēwsa (“a flow, flowing, flux”). Alternatively, perhaps an alteration of Middle English floute, fleute, flote (“a pipe”), see English flute. Compare also Middle Dutch vloegh (“groove, channel, flute of a fluted column”).
Source: English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0), through kaikki.org (Wiktextract).