# sine

/ˈsaɪn/ (US) · /sˈaɪn/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/sine
Updated: 2026-05-31

## Definition

a math term used to describe the relationship between the angles and sides of a right-angled triangle. It is the length of the side opposite an angle divided by the longest side.

For teachers: a trigonometric function representing the ratio of the side opposite a given angle to the hypotenuse in a right-angled triangle.

## Examples

- You need to calculate the sine of the angle to find the height.
- In trigonometry class, students learn how to use the sine function to determine the unknown lengths of triangle sides.
- The oscillation of a pendulum can be modeled using a sine wave, which represents periodic motion as a function of time or distance.

## Usage notes

- Often abbreviated as 'sin' in mathematical notation and formulas.

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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.