# 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’.