Actors joining the French pieces (7)
I believe the answer is:
castles
'pieces' is the definition.
(castle is a kind of piece)
'actors joining the french' is the wordplay.
'actors' becomes 'cast' (group of actors).
'joining' means one lot of letters go next to another.
'the french' becomes 'les' (plural form of 'the' in French).
'cast'+'les'='CASTLES'
(Other definitions for castles that I've seen before include "Fortresses" , "Rooks" , "English homes?" , "Keeps" , "Large and stately mansions" .)