Just on leafy ends (4)
I believe the answer is:
only
'just' is the definition.
(I know that just can be written as only)
'on leafy ends' is the wordplay.
'ends' means to remove the middle letters.
'leafy' with its middle removed is 'ly'.
'on'+'ly'='ONLY'
(Other definitions for only that I've seen before include "Except that; single" , "Exclusive - individual" , "Alone; solitary" , "Siblingless (child)" , "And no one else" .)