Chicken, perhaps rearing a layer (6)
I believe the answer is:
lamina
'a layer' is the definition.
(I've seen this before)
'chicken perhaps rearing' is the wordplay.
'chicken perhaps' becomes 'animal' (chicken is a kind of animal).
'rearing' is a reversal indicator (as in a horse rearing up).
'animal' reversed gives 'LAMINA'.
(Other definitions for lamina that I've seen before include "Thin plate or layer" , "Flat plate" , "Thin plate or scale" .)