Flu or flue?
flu is a noun meaning “Influenza”; flue is a noun meaning “A pipe or duct that carries gaseous combustion products away from the point of…”. They sound the same (/fluː/). In written English (wordfreq, 2021 data) flu is about 15 times as common as flue.
What is the difference between flu and flue?
| flu | flue | |
|---|---|---|
| Part of speech | noun | noun, adjective |
| Meaning | Influenza informalStomach flu | A pipe or duct that carries gaseous combustion products away from the point of combustion (such as a furnace) An enclosed passageway in which to direct a current of air or other gases along |
| Example | catch flu | none recorded |
| Forms | flus | flues |
| Pronunciation | /fluː/ /flʉː/ | /fluː/ [flʉː] /flu/ |
| In writing | 9.1 times per million words | about once in every 2 million words |
Sources: flu and flue in the English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0); written frequency: wordfreq 3.1 (a 2021 snapshot of Wikipedia, subtitles, news, books, web text and social media).
Every current meaning of flu and flue
flu
- 1
Influenza
catch flu
- 2
UKdatedDated form of flu
- 3
informalStomach flu
flue
- 1
A pipe or duct that carries gaseous combustion products away from the point of combustion (such as a furnace)
- 2
UKAlternative form of flew (“shallow, flat”)
- 3
An enclosed passageway in which to direct a current of air or other gases along
- 4
In an organ flue pipe, the opening between the lower lip and the languet
Source: the English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0); obsolete, archaic, dialect and rare senses left out.
Which is more common, flu or flue?
flu appears 9.1 times per million words; flue about once in every 2 million words.
flu 9.1 times per million wordsflue about once in every 2 million words
Source: written frequency: wordfreq 3.1 (a 2021 snapshot of Wikipedia, subtitles, news, books, web text and social media).
How many people search flu vs flue?
“flu vs flue” is searched about 720 times a month on Google and 20 on Bing in the United States. Google counts close variants of a query together (“flue vs flu”, “flu or flue”).
Sources: Google Ads keyword data through DataForSEO and Microsoft Advertising keyword data through DataForSEO, the average month from September 2025 to August 2026.