American throne for English king (4)
I believe the answer is:
john
This clue is a double definition.
'american throne' is the first definition.
(US slang for the toilet or 'throne')
'english king' is the second definition.
(King John, King of England 1199-1216)
'for' is the link.
(Other definitions for john that I've seen before include "Recent popes" , "gospeller" , "From Gwen" , "Magna Carta king" , "toilet" .)