Keep the French behind shed (6)
I believe the answer is:
castle
'keep' is the definition.
(thesaurus)
'the french behind shed' is the wordplay.
'the french' becomes 'le'.
'behind' is a charade indicator (letters next to each other).
'shed' becomes 'cast' (I've seen this before).
'le' after 'cast' is 'CASTLE'.
(Other definitions for castle that I've seen before include "man of 1d [ADVENTURE]" , "Big building" , "Move two pieces" , "''An Englishman's home is his . . .''" , "Man on board" .)