Dull (adjective)

1. Lacking interest or excitement; tedious.
2. Not sharp; blunt.
3. Lacking in brightness or vibrancy; faded.
4. Lacking intelligence or quickness of mind.

Origin:

Middle english dull, from old english dol; related to dutch dof and german dol.

Examples:

1. The lecture was so dull that she fell asleep.
2. The knife was dull and wouldn't cut through the tomato.
3. The colors in the room were dull and uninviting.
4. The dull student struggled to understand the lesson.
5. The day was dull and overcast, with no sun in sight.