Want cash on account for a kilo (4)
I believe the answer is:
lack
'want' is the definition.
(synonyms)
'cash on account for a kilo' is the wordplay.
'cash' becomes 'l' (The pound sterling symbol is an elaborate L).
'on' means one lot of letters go next to another.
'account' becomes 'ac' (abbreviation for account).
'for' is a charade indicator (letters next to each other).
'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)" .)