SINE

noun Etymology: Medieval Latin sinus, from Latin, curve Date: 1593 the trigonometric function that for an acute angle is the ratio between the leg opposite the angle when it is considered part of a right triangle and the hypotenuse, a trigonometric function sin θ that for all real numbers θ is exactly equal to the ~ of an angle of measure θ in radians and that is given by the sum of the alternating series sin θ = θ - θ 3 /3! + θ 5 /5! - θ 7 /7! + θ 9 /9! - . . .