sine

UK: /ˈsaɪn/ US: (sīn)

WordReference Random House Unabridged Dictionary of American English © 2026

sine  (sīn), n. 

1. Mathematics [Trig.]
   • (in a right triangle) the ratio of the side opposite a given acute angle to the hypotenuse.
   • (of an angle) a trigonometric function equal to the ratio of the ordinate of the end point of the arc to the radius vector of this end point, the origin being at the center of the circle on which the arc lies and the initial point of the arc being on the x-axis. Abbr.: sin
2. Mathematics [Geom.] (originally) a perpendicular line drawn from one extremity of an arc of a circle to the diameter that passes through its other extremity.
3. Mathematics (of a real or complex number x) the function sin x defined by the infinite series x - (x³/3!) + (x⁵/5!) - + …, where ! denotes factorial. Cf. cosine (def. 2), factorial (def. 1).

• Sanskrit jiyā, jyā chord of an arc, literally, bowstring
• Neo-Latin, Latin sinus a curve, fold, pocket, translation of Arabic jayb literally, pocket, by folk etymology, etymological
• 1585–95

Collins Concise English Dictionary © HarperCollins Publishers::

sine / saɪn/ noun (of an angle)

1. a trigonometric function that in a right-angled triangle is the ratio of the length of the opposite side to that of the hypotenuse

Etymology: 16th Century: from Latin sinus a bend; in New Latin, sinus was mistaken as a translation of Arabic jiba sine (from Sanskrit jīva, literally: bowstring) because of confusion with Arabic jaib curve

sine / ˈsaɪnɪ/ preposition

1. (esp in Latin phrases or legal terms) lacking; without