# cosine

cosine
[koh-sahyn] /ˈkoʊ saɪn/ Show IPA
nouns 2

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).

1625–35; < Neo-Latin cosinus. See co-, sine1

 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]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
 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