Poetic movement in essence largely blocked by Islamic leader (7)
I believe the answer is:
imagism
'poetic movement' is the definition.
(I've seen this before)
'essence largely blocked by islamic leader' is the wordplay.
'essence' becomes 'gist' (synonyms).
'largely' means to remove the last letter.
'blocked' is an insertion indicator (to block can mean to box in or contain).
'by islamic leader' becomes 'imam' (I can't justify this - if you can you should give a lot more credence to this answer).
'gist' with its final letter taken away is 'gis'.
'gis' going into 'imam' is 'IMAGISM'.
'in' is the link.
Can you help me to learn more?
(Other definitions for imagism that I've seen before include "Poetic movement of the early 20th century" , "C 20 poetic movement" , "movement in poetry" .)