To find the slope of the line connecting the points \( (4, 9) \) and \( (5, 0) \), we use the formula for slope:
\[ m = \frac{y_2 - y_1}{x_2 - x_1} \]
Here, \( (x_1, y_1) = (4, 9) \) and \( (x_2, y_2) = (5, 0) \).
Plugging the values into the formula:
\[ m = \frac{0 - 9}{5 - 4} = \frac{-9}{1} = -9 \]
Thus, the slope of the line is
\[ \boxed{-9} \]