The number of diagonals in a hexagon is 8.

A diagonal is a line segment that joins any two vertices of the polygon and is not a side of the polygon.

A hexagon is a polygon having 6 sides. The diagonals of a hexagon ABCDEF can be drawn as:

The diagonals of the hexagon are $\overline{\mathrm{AC}}, \overline{\mathrm{AD}}, \overline{\mathrm{AE}}, \overline{\mathrm{BD}}, \overline{\mathrm{BE}}, \overline{\mathrm{BF}}, \overline{\mathrm{CE}}, \overline{\mathrm{CF}} \mathrm{and} \overline{\mathrm{DF}}$.

Thus, there are 9 diagonals in a hexagon.