500 homes tidy up mess, say (6,4)
I believe the answer is:
dining room
'mess say' is the definition.
(I know that mess is a type of dining-room)
'500 homes tidy up' is the wordplay.
'500' becomes 'D' (Roman numeral for 500).
'homes' becomes 'inin' (I can't justify this - if you can you should give a lot more credence to this answer).
'tidy up' becomes 'groom' (groom can mean to tidy up or clean).
'd'+'inin'+'groom'='DINING-ROOM'
Can you help me to learn more?
(Other definitions for dining room that I've seen before include "Where meals are eaten" , "place for courses?" , "eating-place" , "refectory" , "mess" .)