An instrument from returned plunder (4)
I believe the answer is:
tool
'an instrument' is the definition.
(I know that tool is a instrument)
'returned plunder' is the wordplay.
'returned' shows that the letters should be reversed in order.
'plunder' becomes 'loot' (synonyms).
'loot' written backwards gives 'TOOL'.
'from' is the link.
(Other definitions for tool that I've seen before include "Utensil; implement" , "Pawn" , "one of 12 [SPADES] , for example" , "Device used for work" , "Practical implement" .)