It's one boring routine (5)
I believe the answer is:
drill
I believe this is a double definition.
'it's one boring' is the first definition.
(I've seen this before)
'routine' is the second definition.
(you know the drill)
(Other definitions for drill that I've seen before include "Exercise by repeated practice - bore" , "strong twilled cotton" , "makes one exercise" , "Stout cotton cloth" , "Make a hole with a pointed tool" .)