Japanese dwarf tree (6)
I believe the answer is:
'japanese dwarf tree' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bonsai that I've seen before include "stunted growth" , "specimen with restricted roots?" , "Japanese craft of growing dwarf trees" , "Japanese art of growing dwarfed trees" , "Japanese method of growing miniature plants" .)