Fancy basin containing round miniature plant (6)
I believe the answer is:
bonsai
'miniature plant' is the definition.
'fancy basin containing round' is the wordplay.
'fancy' indicates an anagram.
'containing' is an insertion indicator.
'round' becomes 'o' (round can mean a round object**).
'basin' is an anagram of 'bnsai'.
'bnsai' enclosing 'o' is 'BONSAI'.
(Other definitions for bonsai that I've seen before include "Japanese method of growing miniature plants" , "Art of growing dwarf varieties of tree" , "Potted tree or shrub artificially prevented from reaching normal size" , "Japanese art of growing dwarfed trees" , "Dwarfed ornamental tree or shrub" .)