# cosine

[ koh-sahyn ]

noun
1. Trigonometry.

• (in a right triangle) the ratio of the side adjacent to a given angle to the hypotenuse.

• the sine of the complement of a given angle or arc. Abbreviation: cos

2. Mathematics. (of a real or complex number x) the function cos x defined by the infinite series 1 − (x2/2!) + (x4/4!) − + …, where ! denotes factorial. Abbreviation: cos: Compare sine (def. 3), factorial (def. 1).

## Origin of cosine

1
1625–35; <New Latin cosinus. See co-, sine

## Words Nearby cosine

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

## How to use cosine in a sentence

• Nevertheless, I bear no grudge against the sine and the cosine, which I continue to hold in high esteem.

The Life of the Fly | J. Henri Fabre
• The nine cosine-inclinations above are, as has been seen, connected by six equations.

## British Dictionary definitions for cosine

cosine

/ (ˈkəʊˌsaɪn) /

noun(of an angle)
1. a trigonometric function that in a right-angled triangle is the ratio of the length of the adjacent side to that of the hypotenuse; the sine of the complement: Abbreviation: cos

## Origin of cosine

1
C17: from New Latin cosinus; see co-, sine 1

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

## Scientific definitions for cosine

cosine

[ sīn′ ]

1. The ratio of the length of the side adjacent to an acute angle of a right triangle to the length of the hypotenuse.

2. The abscissa of the endpoint of an arc of a unit circle centered at the origin of a Cartesian coordinate system, the arc being of length x and measured counterclockwise from the point (1, 0) if x is positive or clockwise if x is negative.

1. A function of a number x, equal to the cosine of an angle whose measure in radians is equal to x.