He is in finest order (6)
I believe the answer is:
behest
'order' is the definition.
(thesaurus)
'he is in finest' is the wordplay.
'is in' indicates putting letters inside.
'finest' becomes 'best' ('best' can be similar in meaning to 'finest').
'he' placed within 'best' is 'BEHEST'.
(Other definitions for behest that I've seen before include "Order" , "Command - Thebes (anag)" , "(At someone's) command" , "Command, bidding" .)