cotangent
noun
co·tan·gent (ˌ)kō-ˈtan-jənt 
ˈkō-ˌtan-
1
: a trigonometric function that for an acute angle is the ratio between the leg adjacent to the angle when it is considered part of a right triangle and the leg opposite
2
: a trigonometric function cot θ that is equal to the cosine divided by the sine for all real numbers θ for which the sine is not equal to zero and is exactly equal to the cotangent of an angle of measure θ in radians
Word History
Etymology
New Latin cotangent-, cotangens, from co- + tangent-, tangens tangent
First Known Use
1635, in the meaning defined at sense 1