Mark cuts grass, uncomplaining (8)
I believe the answer is:
resigned
'uncomplaining' is the definition.
(resigned to one's fate)
'mark cuts grass' is the wordplay.
I cannot really understand how this works, but
'mark' could be 'sign' (synonyms) and 'sign' is located in the answer.
'grass' could be 'reed' (I've seen this before) and 'reed' is found within the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
(Other definitions for resigned that I've seen before include "patient" , "Long-suffering" , "Left work" , "Came to accept with patience" , "Like characters in 5D [WAITING FOR GODOT]" .)