Proprietor with ace houses? Right (5)
I believe the answer is:
owner
'proprietor' is the definition.
('owner' can be a synonym of 'proprietor')
'with ace houses? right' is the wordplay.
'with' becomes 'w' (abbreviation**).
'ace' becomes 'one' ('one' can be a synonym of 'ace').
'houses?' is an insertion indicator.
'right' becomes 'r' (common abbreviation).
'w' put into 'one' is 'owne'.
'owne'+'r'='OWNER'
(Other definitions for owner that I've seen before include "possessive type" , "One who possesses" , "Title holder?" , "landlord" , "Holder, possessor" .)