cosine: Meaning and Definition of

co•sine

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. Abbr.: cos
2. (of a real or complex number x) the function cos x defined by the infinite series 1 − (x/2!) + (x/4!) − + … , where ! denotes factorial. Abbr.: cos Cf. sine (def. 3),(def. 1).