# onset

/ˈɑnˌsɛt/ (US) · /ˈɒnsɛt/ (UK)

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

## Senses

### 1. the start of something unpleasant

noun · CEFR B2

the beginning of something, usually something that is difficult or unwelcome.

For teachers: the beginning or commencement of an event or state, typically one that is unpleasant or problematic.

- The sudden onset of winter caught many people without warm coats.
- The rapid onset of the economic crisis forced the government to implement emergency measures within forty-eight hours.

Usage: Usually follows the pattern 'the onset of [noun]'.

### 2. medical symptoms

noun · CEFR C1 · Technical

the moment when the first signs of an illness appear.

For teachers: the initial phase of a disease or medical condition when symptoms first become apparent to the patient or clinician.

- Early onset of the disease can sometimes be managed with a better diet.
- Clinicians noted that the early onset of symptoms in younger patients often correlated with a more aggressive progression of the underlying infection.

Usage: Often used with adjectives like 'sudden', 'gradual', or 'early'.

### 3. linguistics

noun · CEFR C2 · Technical · Academic

the first part of a syllable, before the main vowel sound.

For teachers: the initial consonant or consonant cluster of a syllable, preceding the nucleus.

- In the word 'stop', the letters 'st' form the onset.
- The researcher analyzed how children acquire complex onsets in languages that allow three or more consonants before the vowel nucleus.

Usage: Used specifically in phonology to describe syllable structure.

### 4. a military attack

noun · CEFR C2 · Archaic · Literary

a sudden and fierce attack by an army.

For teachers: a military assault or a sudden, violent attack.

- The soldiers prepared themselves for the enemy's fierce onset at dawn.
- The fortress walls eventually crumbled under the repeated onset of the heavy cavalry and the relentless bombardment of the siege engines.

Teaching tip: This sense is rare in modern speech; learners will mostly encounter it in historical novels or older poetry.

## Examples

- The onset of winter brought heavy snow.
- Early treatment is most effective if started immediately after the onset of symptoms.
- The sudden onset of the economic crisis caught many investors off guard, leading to a rapid sell-off in global markets.

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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.