The shaky rotter's rude reply (6)
I believe the answer is:
retort
'rude reply' is the definition.
'retort' can be an answer for 'reply' (retort is a kind of reply). I am not certain of the 'rude' bit.
'the shaky rotter's' is the wordplay.
'the shaky' indicates an anagram.
'rotter' with letters rearranged gives 'RETORT'.
Can you help me to learn more?
(Other definitions for retort that I've seen before include "Riposte, reply" , "Witty reply" , "Rotter (anag.)" , "A sharp reply or vessel used in distilling" , "Sharp riposte" .)