Close the gap almost filled with eastern plant extract (7)
I believe the answer is:
catechu
'plant extract' is the definition.
(I've seen this before)
'close the gap almost filled with eastern' is the wordplay.
'close the gap' becomes 'catch up' (I've seen this in another clue).
'almost' means to remove the last letter (most of the word but not all of it).
'filled with' means one lot of letters goes inside another.
'eastern' becomes 'e'.
'catchup' with its last letter taken away is 'catchu'.
'catchu' enclosing 'e' is 'CATECHU'.
(Other definitions for catechu that I've seen before include "source of tannin" , "Plant extract" .)