Want cash on account for a kilo (4)
I believe the answer is:
lack
'want' is the definition.
('lack' can be a synonym of 'want')
'cash on account for a kilo' is the wordplay.
'cash' becomes 'l' (The pound sterling symbol is an elaborate L**).
'on' is a charade indicator (letters next to each other).
'account' becomes 'ac'.
'for' means one lot of letters go next to another.
'a kilo' becomes 'k' (phonetic alphabet: alpha, bravo, charlie etc.).
'l'+'ac'+'k'='LACK'
(Other definitions for lack that I've seen before include "Be without, need" , "Be without or short of" , "Shortage" , "Dearth" , "Deficiency (of something)" .)