Drilling is uninteresting (6)
I believe the answer is:
boring
This clue is a double definition.
'drilling' is the first definition.
('bore' can be a synonym of 'drill')
'uninteresting' is the second definition.
(similar in meaning)
'is' acts as a link.
(Other definitions for boring that I've seen before include "Drilling can be tedious" , "Tedious, tiresome" , "Mentally wearying" , "like watching paint dry?" , "flat" .)