- the ratio of the opposite side of a given acute angle in a right triangle to the hypotenuse
- an equivalent, positive or negative ratio for certain related angles (Ex.: the sine of 57° or 123° is .8387, of 237° or 303° is ?.8387) or real numbers representing radians (Ex.: the sine of .9948 radians (57°) is .8387)

Origin of sine

Medieval Latin*sinus*( from L, a bend, curve, hanging fold of a toga), used as translated, translation of Arabic

*jaib*, sine, bosom of a garment