cosine Hear it!

cosine definition

co·sine (kō′sīn′)

noun

the reciprocal of the secant; specif.
  1. the ratio of the adjacent side of a given acute angle in a right triangle to the hypotenuse
  2. 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)

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

Webster's New World College Dictionary Copyright © 2005 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.

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