Laborious routine in mill? (5)
I believe the answer is:
grind
I believe this is a double definition.
'laborious routine' is the first definition.
(I've seen this in another clue)
'mill?' is the second definition.
(I know that mill can be written as grind)
'in' is the link.
(Other definitions for grind that I've seen before include "Harshly rub together" , "hard slog" , "Wear down" , "Laborious work" , "Wearisome task" .)