Making holes is dull (6)
I believe the answer is:
boring
I believe this is a double definition.
'making holes' is the first definition.
(I've seen this before)
'dull' is the second definition.
(I know that dull can be written as boring)
'is' acts as a link.
(Other definitions for boring that I've seen before include "Tedious, tiresome" , "flat" , "Dull and repetitive, a turn-off" , "Making holes" , "Tedious, of no interest" .)