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# cosine

[koh-sahyn] /ˈkoʊ saɪn/
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 − (x 2 /2!) + (x 4 /4!) − + …, where ! denotes factorial.
Abbreviation: cos.
Compare sine (def 3), factorial (def 1).
Origin of cosine
1625-1635
1625-35; < New Latin cosinus. See co-, sine
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for cosine
Historical Examples
• Like the functions sine and cosine, the elliptic functions have addition theorems, e.g.

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

Anthon Bernhard Elias Nilsen
• These are then respectively the sine and cosine of the angle α between the radius and one of the axes (O X).

Thomas Commerford Martin
• Multiply this by the cosine of the angle and divide by the sine, and we shall get the value of the arc QY for the equator.

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

J. Henri Fabre
• The sine and the cosine I shall have occasion to employ in the latter part of my lecture.

• Here then was the sine of an arc which did not recognize equality in the cosine of its supplement.

Henry A. Castle
• Integrators were of three kinds: radius machines; cosine machines; tangent machines.

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 cos
Word Origin
C17: from New Latin cosinus; see co-, sine1
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for cosine
n.

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

Online Etymology Dictionary, © 2010 Douglas Harper
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cosine in Science
 cosine   (kō'sīn')    The ratio of the length of the side adjacent to an acute angle of a right triangle to the length of the hypotenuse.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.A function of a number x, equal to the cosine of an angle whose measure in radians is equal to x.
The American Heritage® Science Dictionary