n.
Pronunciation: ' s ī n
Function: noun
Etymology: Medieval Latin sinus, from Latin, curve
Date: 1593
1 : 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
2 : a trigonometric function sin θ that for all real numbers θ is exactly equal to the sine 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!) - ⋯