Drills are so dull (6)
I believe the answer is:
boring
'dull' is the definition.
(I know that dull can be written as boring)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for boring that I've seen before include "Dull and repetitive, a turn-off" , "flat" , "like watching paint dry?" , "Drilling - it's monotonous" , "Making holes" .)