Tiresome grind (3)
I believe the answer is:
rut
'tiresome grind' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rut that I've seen before include "occupying male deer in autumn" , "Groove or routine" , "Wheel-furrow" , "deer find it exciting" , "spell of arousal" .)