Definitions
from The American Heritage® Dictionary of the English Language, 5th Edition.
 noun In a right triangle, the ratio of the length of the side adjacent to an acute angle to the length of the hypotenuse.
 noun The abscissa at 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.
from The Century Dictionary.
 noun In trigonom., the sine of the complement of a given angle (whose cosine it is).
from the GNU version of the Collaborative International Dictionary of English.
 noun (Trig.) The sine of the complement of an arc or angle. See
Illust. offunctions .
from Wiktionary, Creative Commons Attribution/ShareAlike License.
 noun trigonometry In a
right triangle , theratio of thelength of theside adjacent to anacute angle to the length of thehypotenuse . Symbol:cos
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
 noun ratio of the adjacent side to the hypotenuse of a rightangled triangle
Etymologies
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Examples

Measuring Relational Similarity with VSM The measure of similrity of R1 and R2 is given by the cosine of the angle Ɵ between r1 and r2: cosine = ∑ r1, i. r2, i = r1. r2 = r1. r2

So, if the current is sinusoidal, you know the derivative of a sine to be a cosine, which is 90° out of phase.
unknown title 2008

Did you know that it's possible to calculate a cosine even if you think "cosine" is a brand of nasal decongestant?

Did you know that it's possible to calculate a cosine even if you think "cosine" is a brand of nasal decongestant?

And so the sine and cosine are both negative multiples of their own second derivatives (in fact, the factor is – 1).

And so the sine and cosine are both negative multiples of their own second derivatives (in fact, the factor is – 1).

Starting from algebraic operations and simple analytical functions such as sine and cosine, the algorithm randomly recombines previous equations and parameters, and tests each set of expressions for accuracy against the empirical data, until it reaches a desired level of accuracy.
Archive 20090401 Gordon McCabe 2009

Laboring in the House of Wisdom, alKhwarizmi, a Persian by birth, combined the geometry of triangles and spheres with the verbal elaboration of equations to work out the first sine and cosine tables.
Clay Farris Naff: A Moment Of Opportunity For Muslims Clay Farris Naff 2011

He reminded me of sine and cosine and complementary angles, all of which were things I believed in and knew to be true.
Chocolate & Vicodin Jennette Fulda 2011

He reminded me of sine and cosine and complementary angles, all of which were things I believed in and knew to be true.
Chocolate & Vicodin Jennette Fulda 2011
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