If something is dull, it’s boring, uneventful, or monotonous:
The movie was so dull I feel asleep.
This class is dull. The teacher needs to liven things up a bit.
Maria has a dull job. She does the same thing eight hours a day.
This has been kind of a dull day.
Grey and brown are dull colors.
Jim has had a dull ache in his stomach for the last few months. He should see a doctor. ("A dull ache" is small, constant pain that might come and go.)
We also use the word "dull" when the edge of a knife or any other object used for cutting is not sharp:
This knife is dull. It doesn’t cut through the meat very easily.
