# caffeine

/kæˈfin/ (US) · /kˈæfiːn/ (UK) · CEFR B1 · Noun

Source: https://englishreference.com/word/caffeine
Updated: 2026-05-03

## Definition

a natural substance found in coffee and tea that makes you feel more awake and energetic.

For teachers: a bitter, white crystalline alkaloid that acts as a central nervous system stimulant. Found naturally in the seeds, leaves, and fruit of various plants, it is most commonly consumed in coffee, tea, and soft drinks.

## Examples

- I try not to drink any caffeine after four in the afternoon.
- Many people rely on a morning dose of caffeine to help them focus and feel alert during early meetings.
- While moderate consumption of caffeine is generally considered safe, excessive intake can lead to jitteriness, increased heart rate, and disrupted sleep patterns in sensitive individuals.

## Usage notes

- Uncountable when referring to the substance in general; occasionally countable in informal speech when referring to a serving of a caffeinated drink.

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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.