noun 1.Trigonometry.a.(in a right triangle) the ratio of the side adjacent to a given angle to the hypotenuse.
b.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 − (
x ^{2} /2!) + (
x ^{4} /4!) − + …, where ! denotes factorial.
Abbreviation: cos Compare
sine ( def 3 ),
factorial ( def 1 ).
Origin: 1625–35; <
Neo-Latin cosinus. See
co-,
sine^{1}