King in decline complaining (7)
I believe the answer is:
railing
'complaining' is the definition.
(railing is a kind of complaining)
'king in decline' is the wordplay.
I cannot really see how this works, but
'king' could be 'r' (abbreviation of Latin rex) and 'r' is present in the answer.
'in' is present in the answer.
'decline' could be 'ail' (I've seen this in other clues) and 'ail' is located in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for railing that I've seen before include "complaints procedure?" , "Haranguing -- horizontal bar on supports" , "Iron barrier" , "Metal barrier" , "Fencing - complaining - attacking" .)