Ruthless daily grind at a mundane line? (3)
I believe the answer is:
rut
'ruthless daily grind' is the definition.
'rut' can be an answer for 'grind' (thesaurus). I'm not certain of the 'ruthless daily' bit.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rut that I've seen before include "It can be frustrating" , "mate" , "Deep tyre track" , "Deep groove as in a lane" , "Deep vehicle track" .)