Organ Saracen moved with foremost of props (8)
I believe the answer is:
pancreas
'organ' is the definition.
(pancreas is a kind of organ)
'saracen moved with foremost of props' is the wordplay.
'moved with' is an anagram indicator.
'foremost of' says to take the initial letters.
The first letter of 'props' is 'p'.
'saracen' with its letters mixed up with 'p' gives 'PANCREAS'.
(Other definitions for pancreas that I've seen before include "organ" , "Large gland behind the stomach" , "Gland aiding digestion" , "It secretes insulin" , "Sweetbread" .)