Definition of sine
1
: the trigonometric function that for an acute angle is the ratio between the leg opposite the angle when it is considered part of a right triangle and the hypotenuse
2
: a trigonometric function sin θ that for all real numbers θ is exactly equal to the sine of an angle of measure θ in radians and that is given by the sum of the alternating series {latex}\sin \theta = \theta  \frac{\theta^{3}}{3!} + \frac{\theta^{5}}{5!}  \frac{\theta^{7}}{7!} + \frac{\theta^{9}}{9!}  \dots{/latex}
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MerriamWebster unabridged
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Time Traveler for sine
The first known use of sine was in 1593
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