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 (almost the whole word is kept).
'filled with' is an insertion indicator.
'eastern' becomes 'e'.
'catchup' with its last letter taken off is 'catchu'.
'catchu' going around 'e' is 'CATECHU'.
(Other definitions for catechu that I've seen before include "source of tannin" , "Plant extract" .)