Wood covering empty mango's top ... (8)
I believe the answer is:
foremost
'top' is the definition.
('foremost' can be a synonym of 'top')
'wood covering empty mango's' is the wordplay.
'wood' becomes 'forest' ('forest' can be a synonym of 'wood'**).
'covering' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'mango' with its middle removed is 'mo'.
'forest' placed around 'mo' is 'FOREMOST'.
(Other definitions for foremost that I've seen before include "First in time, place or order" , "Pre-eminent" , "top" , "Most prominent" , "First in time, place or importance" .)