# co-sine

## cosine

[koh-sahyn]
noun
1.
Trigonometry.
a.
(in a right triangle) the ratio of the side adjacent to a given angle to the hypotenuse.
b.
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:
1625–35; < Neo-Latin cosinus. See co-, sine1

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World English Dictionary
 cosine (ˈkəʊˌsaɪn) —n cos 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 [C17: from New Latin cosinus; see co-, sine1]

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Etymonline
Word Origin & History

cosine
1630s, from co- + sine.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
 cosine   (kō'sīn')  Pronunciation Key  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