Constant suffering (7)
I believe the answer is:
abiding
This clue is a double definition.
'constant' is the first definition.
(I've seen this in another clue)
'suffering' is the second definition.
('abide' can be a synonym of 'suffer')
(Other definitions for abiding that I've seen before include "Putting up with: long-lasting" , "Durable, lasting" , "firm" , "Stopping" , "bearing" .)