cosine

[koh-sahyn]
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 cosine

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

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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 for cosine

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 for cosine
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.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.