# flu

/ˈfɫu/ (US) · /flˈuː/ (UK)

Source: https://englishreference.com/word/flu
Updated: 2026-06-20

## Senses

### 1. influenza

noun · CEFR A2

a common illness that gives you a fever, a headache, and makes your muscles ache.

For teachers: an acute respiratory infection caused by influenza viruses. Uncountable in general usage; often takes the definite article 'the'.

- I couldn't go to work because I had the flu and a high fever.
- Public health officials urged vulnerable populations to receive their vaccinations before the flu season reached its peak in mid-winter.

Usage: Usually used with the definite article 'the'.

### 2. stomach illness

noun · CEFR B1 · Informal

an illness that makes you feel sick to your stomach, often causing vomiting.

For teachers: a colloquial term for gastroenteritis or similar digestive upsets, though medically distinct from influenza.

- Half the kids in the class were out last week with a stomach flu.
- Although the patient described his symptoms as 'stomach flu', the physician suspected a bacterial infection from contaminated seafood.

Teaching tip: Medical professionals prefer 'gastroenteritis' as 'flu' technically only refers to respiratory viruses.

## Examples

- I stayed in bed all week because I had the flu.
- The office was half-empty today because a nasty strain of flu is going around the city.
- Public health officials monitor seasonal flu patterns closely to ensure that the annual vaccine remains effective against the most prevalent circulating strains.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.