Heightening arrangement of henna on binder (11)
I believe the answer is:
enhancement
'heightening' is the definition.
(I've seen this before)
'arrangement of henna on binder' is the wordplay.
'arrangement of' indicates anagramming the letters.
'on' means one lot of letters go next to another.
'binder' becomes 'cement' (I've seen this before).
'henna' with letters rearranged gives 'enhan'.
'enhan'+'cement'='ENHANCEMENT'
(Other definitions for enhancement that I've seen before include "Improving change" , "Improvement in quality" , "Heightening" , "Boost, intensification" , "What improves" .)