Brute's thin plate backfired (6)
I believe the answer is:
animal
'brute's' is the definition.
('animal' can be a synonym of 'brute')
'thin plate backfired' is the wordplay.
'thin plate' becomes 'lamina' (I've seen this before).
'backfired' shows that the letters should be reversed in order.
'lamina' written backwards gives 'ANIMAL'.
(Other definitions for animal that I've seen before include "Uncivilised person" , "Possibly bear" , "Any organism capable of voluntary movement" , "swine" , "It shares the world with vegetable and mineral" .)