枯燥 (kū zào): dry, boring

Repeating the same security-check movements every day, the job gradually became dull, so he had to rely on listening to music to stay alert.

The content of this grammar book is dry; I read for less than ten minutes before I was so sleepy I fell asleep on the desk.

After Grandpa retired, he felt that staying at home all day was too dull, so he signed up for the community calligraphy class.

To make the dull meeting more interesting, the manager added some funny short videos to the slides.