Answer
$-\dfrac{\sqrt{3}}{2}$
Work Step by Step
The sine is an odd function, so
$\sin{(-\theta)} = - \sin{\theta}$
Thus,
$\sin{\left(- \dfrac{\pi}{3} \right) } = - \sin{\left( \dfrac{\pi}{3} \right) } = \boxed{-\dfrac{\sqrt{3}}{2}}$