Chicken cut up, cooked or not (8)
I believe the answer is:
poltroon
'chicken' is the definition.
(thesaurus)
'cut up cooked or not' is the wordplay.
'cut' becomes 'lop' (lopping is a kind of cutting**).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'cooked' indicates an anagram.
'lop' reversed gives 'pol'.
'or'+'not'='ornot'
'ornot' is an anagram of 'troon'.
'pol'+'troon'='POLTROON'
(Other definitions for poltroon that I've seen before include "Traditional chicken" , "one was entirely yellow" , "Abject coward" , "Utter coward" .)