What is "sine of an angle"

Sine \Sine\, n. [LL. sinus a sine, L. sinus bosom, used in translating the Ar. jaib, properly, bosom, but probably read by mistake (the consonants being the same) for an original j[=i]ba sine, from Skr. j[=i]va bowstring, chord of an arc, sine.] (Trig.)

1. The length of a perpendicular drawn from one extremity of an arc of a circle to the diameter drawn through the other extremity.

2. The perpendicular itself. See Sine of angle, below.

   Artificial sines, logarithms of the natural sines, or logarithmic sines.

   Curve of sines. See Sinusoid.

   Natural sines, the decimals expressing the values of the sines, the radius being unity.

   Sine of an angle, in a circle whose radius is unity, the sine of the arc that measures the angle; in a right-angled triangle, the side opposite the given angle divided by the hypotenuse. See Trigonometrical function, under Function.

   Versed sine, that part of the diameter between the sine and the arc.