Keep French article under shed (6)
I believe the answer is:
castle
'keep' is the definition.
(I've seen this before)
'french article under shed' is the wordplay.
'french article' becomes 'le' (definite article in French).
'under' says to put letters next to each other (below, in a down clue).
'shed' becomes 'cast' (shed can mean to discard or cast off).
'le' after 'cast' is 'CASTLE'.
(Other definitions for castle that I've seen before include "Make chess move involving king and rook" , "Move two pieces" , "Keep" , "Move king to safety - stronghold" , "Move rook and king in the same turn" .)