I. ˈsīn noun
( -s )
Etymology: Medieval Latin sinus (intended, under influence of Arabic jaib curve, as translation of Arabic jiba sine, from Sanskrit jīva bowstring, chord of an arc), from Latin, curve, fold — more at sinus
: the y coordinate of any point except the vertex on the terminal side of an angle divided by the distance between the vertex and the point, the vertex coinciding with the origin of a plane rectangular coordinate system and the initial side of the angle coinciding with the positive x-axis
II. noun
: 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! - . . .