In a cult, going mad. Quite mad (7)
I believe the answer is:
lunatic
'quite mad' is the definition.
'lunatic' can be an answer for 'mad' (I've seen this before). I'm unsure of the 'quite' bit.
'in a cult going mad' is the wordplay.
'going mad' indicates anagramming the letters.
'in'+'a'+'cult'='inacult'
'inacult' with letters rearranged gives 'LUNATIC'.
Can you help me to learn more?
(Other definitions for lunatic that I've seen before include "Maniac" , "Bats" , "Crazy" , "Harebrained" , "Mad" .)