Pieces concealed by farm subsidies (4)
I believe the answer is:
arms
'pieces' is the definition.
(arm is a kind of piece)
'concealed by farm subsidies' is the wordplay.
'concealed' indicates the answer is hidden within the clue.
'ARMS' is hidden within 'by farm subsidies'.
(Other definitions for arms that I've seen before include "Protesting violently, up in these" , ". . . . and The Man (G.B. Shaw)" , "military equipment" , "International competition for weapons" , "Supplies weapons" .)