Greets an alternative officer (8)
I believe the answer is:
sergeant
'officer' is the definition.
(I know that Sergeant is a type of Japanese police officer)
'greets an alternative' is the wordplay.
'alternative' is an anagram indicator (an alternative ordering of the letters).
'greets'+'an'='greetsan'
'greetsan' is an anagram of 'SERGEANT'.
(Other definitions for sergeant that I've seen before include "military man" , "NCO; Death a fell one, Hamlet" , "Man in charge" , "Estrange from junior army officer" , "Estrange (anag)" .)