A contractile organ of the body (6)
I believe the answer is:
muscle
'a contractile organ of the body' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for muscle that I've seen before include "Body tissue that expands and contracts" , "meat" , "Body tissue that effects movement" , "Fibrous tissue in the body" , "Bicep or tricep, for instance" .)