Call idiot in Asian capital (7)
I believe the answer is:
ringgit
'asian capital' is the definition.
(currency of Malaysia)
'call idiot' is the wordplay.
'call' becomes 'ring' (telephone call).
'idiot' becomes 'git'.
'ring'+'git'='RINGGIT'
'in' is the link.
(Other definitions for ringgit that I've seen before include "Malaysian currency" , "Standard monetary unit of Malaysia" , "capital of Malaysia" , "Asian cash" , "Ready in Kuala Lumpur" .)