Landlord initially gets in double rent (5)
I believe the answer is:
split
'rent' is the definition.
('split' can be a synonym of 'rent')
'landlord initially gets in double' is the wordplay.
'initially' suggests taking the first letters.
'gets in' is an insertion indicator.
'double' becomes 'spit' (I've seen this before).
The initial letter of 'landlord' is 'l'.
'l' inserted within 'spit' is 'SPLIT'.
(Other definitions for split that I've seen before include "shared by a couple?" , "Cavil" , "See 9" , "Left" , "Separate or cut with a tool" .)