They are tedious drills (5)
I believe the answer is:
bores
'drills' is the definition.
('bore' can be a synonym of 'drill')
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for bores that I've seen before include "Makes a hole with a pointed tool" , "Tedious people or drills" , "Dull tedious talkers" , "Drills or wearies" .)