sine

American  

[sahyn] / saɪn /

noun

1. Trigonometry.

   1. (in a right triangle) the ratio of the side opposite a given acute angle to the hypotenuse.

   2. (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. sin

2. Geometry. (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 numberx ) the function sin x defined by the infinite series x − (x 3 /3!) + (x 5 /5!) − + …, where ! denotes factorial.

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sine ¹ British  

/ ˈsaɪnɪ /

preposition

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

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sine ² British  

/ saɪn /

noun

1.  sin. 

   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

   2. a function that in a circle centred at the origin of a Cartesian coordinate system is the ratio of the ordinate of a point on the circumference to the radius of the circle

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sine Scientific  

/ sīn /

1. The ratio of the length of the side opposite an acute angle in a right triangle to the length of the hypotenuse.

2. The ordinate of the endpoint of an arc of a unit circle centered at the origin of a Cartesian coordinate system, the arc being of length x and measured counterclockwise from the point (1, 0) if x is positive or clockwise if x is negative.

3. A function of a number x, equal to the sine of an angle whose measure in radians is equal to x.

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Etymology

Origin of sine

1585–95; < New Latin, Latin sinus a curve, fold, pocket, translation of Arabic jayb literally, pocket, by folk etymology < Sanskrit jiyā, jyā chord of an arc, literally, bowstring

Example Sentences

This is the sine qua non of self-defense.

From The Wall Street Journal • Mar. 12, 2026

Fosse suggests, through the Emcee, that though the West’s relationship to queerness may bear the pattern of a sine wave, the Grande Human Cabaret can never metaphorically or spiritually close.

From Salon • Oct. 4, 2025

Glasnow has been out sine April 28 with shoulder discomfort.

From Los Angeles Times • Jul. 6, 2025

But a first hostage deal “is the sine qua non of the administration’s larger regional deal,” said Martin S. Indyk, a former U.S. ambassador to Israel.

From New York Times • Jan. 25, 2024

It was as though he knew very well that in Lombard's past actions legality had not always been a sine qua non....

From "And Then There Were None" by Agatha Christie