Grumble incessantly about watch (7)
I believe the answer is:
chunter
'grumble' is the definition.
(I've seen this before)
'incessantly about watch' is the wordplay.
'incessantly about' becomes 'c' (circa abbreviation. I am not sure about the 'incessantly' bit.).
'watch' becomes 'hunter' (type of watch).
'c'+'hunter'='CHUNTER'
Can you help me to learn more?
(Other definitions for chunter that I've seen before include "Rabbit" , "Go on" , "Mutter" , "beef" , "Grumble monotonously" .)