Complaining about the rain - sick of it (7)
I believe the answer is:
railing
'complaining' is the definition.
(railing is a kind of complaining)
'the rain sick of it' is the wordplay.
I cannot really see how this works, but
'sick' could be 'ailing' (similar in meaning) and 'ailing' is present in the answer.
A single letter 'r' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'about' is the link.
Can you help me to learn more?
(Other definitions for railing that I've seen before include "Complaining bitterly - barrier" , "Using abusive language" , "Annoying" , "barrier appears" , "complaints procedure?" .)