Robber in bottom flat? (7)
I believe the answer is:
footpad
'robber' is the definition.
(I've seen this before)
'bottom flat?' is the wordplay.
'bottom' becomes 'foot' (foot is a kind of bottom).
'flat?' becomes 'pad' (a person's home).
'foot'+'pad'='FOOTPAD'
'in' acts as a link.
(Other definitions for footpad that I've seen before include "Horseless highwayman" , "Mugger of old" , "thief?" , "Old robber" , "Highwayman without a horse" .)