Arising beast - a layer! (6)
I believe the answer is:
lamina
'a layer' is the definition.
(I've seen this before)
'arising beast' is the wordplay.
'arising' says the letters should be written backwards.
'beast' becomes 'animal' (a beast is an animal).
'animal' reversed gives 'LAMINA'.
(Other definitions for lamina that I've seen before include "Flat plate" , "Thin plate or layer" , "Thin plate or scale" .)