definitions
• synonyms

# cosine

[koh-sahyn]
See more synonyms on Thesaurus.com
noun
1. Trigonometry.
1. (in a right triangle) the ratio of the side adjacent to a given angle to the hypotenuse.
2. 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: cosCompare sine(def 3), factorial(def 1).

## Origin of .css-1fxfie5{font-size:22px;}@media (max-width:768px){.css-1fxfie5{font-size:18px;margin:0 10px 10px 0;word-break:break-all;word-wrap:break-word;-webkit-hyphens:auto;-moz-hyphens:auto;-ms-hyphens:auto;hyphens:auto;line-height:22px;}}cosine

1625–35; < New Latin cosinus. See co-, sine
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

## Examples from the Web for cosine

### Historical Examples

• #### Like the functions sine and cosine, the elliptic functions have addition theorems, e.g.

The New Gresham Encyclopedia

Various

• #### And, seating himself beside Dirrik, he began to explain the mysteries of sine, cosine and tangent.

Dry Fish and Wet

Anthon Bernhard Elias Nilsen

• #### 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

British Dictionary definitions for cosine

# cosine

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 complementAbbreviation: cos

## Word Origin

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

## Word Origin and History forcosine

### n.

1630s, from co. sinus, abbreviation of Medieval Latin complementi sinus (see complement + sine).

Online Etymology Dictionary, © 2010 Douglas Harper

cosine in Science

# cosine

[kōsīn′]
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.
3. A function of a number x, equal to the cosine of an angle whose measure in radians is equal to x.