Old, empty toilet in prison house (7)
I believe the answer is:
cottage
'house' is the definition.
(cottage is a kind of house)
'old empty toilet in prison' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'empty' says to hollow out the word (remove centre letters).
'in' means one lot of letters goes inside another.
'prison' becomes 'cage' (I've seen this before**).
'toilet' with its centre removed is 'tt'.
'o'+'tt'='ott'
'ott' placed inside 'cage' is 'COTTAGE'.
(Other definitions for cottage that I've seen before include "simple accommodation" , "Small house with a single storey" , "bungalow" , "Small house, in the country say" , "Modest accommodation" .)