Familiar form of English city rising initially behind houses (4)
I believe the answer is:
brum
'familiar form of english city' is the definition.
(informal name for Birmingham)
'rising initially behind houses' is the wordplay.
'initially' indicates taking the first letters.
'behind' becomes 'bum' (synonyms).
'houses' indicates putting letters inside.
The first letter of 'rising' is 'r'.
'r' put inside 'bum' is 'BRUM'.
(Other definitions for brum that I've seen before include "Birmingham (informal)" , "Birmingham (abbr)" , "Birmingham's nickname" , "Birmingham (abbrev.)" .)