# cosine

> English word · Noun · IPA /ˈkəʊ.saɪn/ · frequency rank #52,240

## Definitions
1. In a right triangle, the ratio of the length of the side adjacent to an acute angle to the length of the hypotenuse. Symbol: cos

## Etymology
From co- + sine, short for complementi sinus in Latin, meaning “sine of the complement”. Doublet of cosinus.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/cosine