(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. Abbreviation: sin
Geometry. (originally) a perpendicular line drawn from one extremity of an arc of a circle to the diameter that passes through its other extremity.
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.Compare cosine(def 2), factorial(def 1).
The ratio of the length of the side opposite an acute angle in a right triangle to the length of the hypotenuse.
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.
A function of a number x, equal to the sine of an angle whose measure in radians is equal to x.
The essential, crucial, or indispensable ingredient without which something would be impossible: “Her leadership was the sine qua non of the organization's success.” From Latin, meaning “without which nothing.”
An essential element or condition, as in A perfect cake is the since qua non of a birthday party. This phrase is Latin for “without which not” and has been used in English since about 1600. It appears more in writing than in speech.