Type of residence (4)
There are a few possibilities for this:
apartment
(Other definitions for flat that I've seen before include "lacking in taste" , "like some races" , "12 [TWO DIMENSIONAL]" , "Even -- pitched too low" , "Prostrate" .)
(Other definitions for semi that I've seen before include "A whole house (or half?)" , "Prefix meaning half (4)" , "Residence" , "match, the last but one?" , "Type of house (UK) - type of truck (US)" .)
(Other definitions for apartment that I've seen before include "pad" , "Flat (chiefly US)" , "quarters" , "place to live" , "Suite of rooms to live in" .)