Rage about the extremity of Japanese flower arrangement (6)
I believe the answer is:
wreath
'flower arrangement' is the definition.
(I know that wreath is a type of flower arrangement)
'rage about the extremity of japanese' is the wordplay.
'rage' becomes 'wrath' (I've seen this in another clue).
'about' is an insertion indicator.
'the extremity of japanese' becomes 'e' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'wrath' enclosing 'e' is 'WREATH'.
Can you help me to learn more?
(Other definitions for wreath that I've seen before include "outdoor Christmas decoration" , "A circle made of flowers and leaves" , "Circular band of flowers and leaves, often seen on graves" , "Circle of flowers used at funerals" , "Circle of flowers or foliage" .)