Depression, at length, can be merely routine (3)
I believe the answer is:
rut
I believe this is a quadruple definition!!
'depression' is the first definition.
(I know that rut is a type of channel)
'at' is a link.
'length can' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'be' is the third definition.
(rutting is a kind of being)
'merely routine' is the fourth definition.
'rut' can be an answer for 'routine' (being stuck in a rut is being stuck in a routine). I am unsure of the 'merely' bit.
Can you help me to learn more?
(Other definitions for rut that I've seen before include "Wheel-furrow" , "animal passion" , "Well-worn track" , "Oestrus" , "hazard in the road" .)