# sine

## Definitions

### General Science

- noun a trigonometric function equal to the length of the side opposite to an angle in a right-angled triangle divided by the hypotenuse

### Electronics

- For a right
__triangle__, the__ratio__of the length of the side opposite to an acute angle, to the length of the hypotenuse. This contrasts with cosine, which is the ratio of the length of the side__adjacent__to an acute angle, to the length of the hypotenuse.

## Origin & History of “sine”

As in the

__case__of__many____other__mathematical terms,__English__is indebted to Arabic for*sine*. But__here__the debt is__only____semantic__, not formal. The word*sine*itself was borrowed from Latin*sinus*‘curve,__fold__, hollow’ (source__also__of English*sinuous*(16^{th}c.) and indeed of*sinus*(16^{th}c.), whose anatomical use comes from the notion of a ‘hollow’ place or cavity). In__post__-classical times it came to denote the ‘fold of a garment’, and so it was mistakenly used to translate Arabic*jayb*‘chord of an arc’, a__doppelganger__of Arabic*jayb*‘fold of a garment’.