Piece I have taken with pawn in retaliation (8)
I believe the answer is:
punitive
'in retaliation' is the definition.
(as in a punitive measure)
'piece i have taken with pawn' is the wordplay.
'piece' becomes 'unit' (I have seen 'Piece of furniture' mean 'unit' so perhaps 'piece' could also mean 'unit').
'i have' becomes 'I've' (contraction of 'I have').
'taken with' means one lot of letters go next to another.
'pawn' becomes 'p'.
'unit'+'ive'='unitive'
'unitive' put after 'p' is 'PUNITIVE'.
(Other definitions for punitive that I've seen before include "very demanding" , "Inflicting penalties" , "Severe and retaliatory" , "As deterrent, retribution" , "Inflicting penalty for an offence" .)