Japanese move ousting British arbiter (5)
I believe the answer is:
judge
'arbiter' is the definition.
(a judge arbitrates)
'japanese move ousting british' is the wordplay.
'japanese' becomes 'J' (international code for Japanese vehicles).
'move' becomes 'budge' (to budge is to move slightly).
'ousting' indicates named letters should be taken away.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'budge' with 'b' taken out is 'udge'.
'j'+'udge'='JUDGE'
(Other definitions for judge that I've seen before include "Estimate" , "Form an opinion of" , "Arbitrator" , "Senior officer of the law" , "rule" .)