cosine

(kō′sīn′)

noun

the reciprocal of the secant; specif.

the ratio of the adjacent side of a given acute angle in a right triangle to the hypotenuse
an equivalent, positive or negative ratio for certain related angles (Ex.: the cosine of 57° or 303° is .5446, of 123° or 237° is -.5446) or real numbers representing radians (Ex.: cosine of .9948 radians (57°) is .5446)

Origin: ModL < co. sinus, short for complementi sinus, lit., sine of the complement

See cosine in American Heritage Dictionary 4

noun Abbr. cos

In a right triangle, the ratio of the length of the side adjacent to an acute angle to the length of the hypotenuse.
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.

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