Monotonous routine (3)
I believe the answer is:
rut
'monotonous routine' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rut that I've seen before include "excitement in male deer" , "Wheel-furrow" , "Deep worn track, a bad place to be" , "predictable course" , "Track made by wheels" .)