Sinew (6)
I believe the answer is:
tendon
'sinew' is the definition.
(I know that sinew can be written as tendon)
This is all the clue.
(Other definitions for tendon that I've seen before include "Strong tissue cord connecting muscles" , "Strong band of tissue connecting muscles" , "Fibrous tissue attaching muscle to bone" , "Fibrous band" , "Strong tissue that connects muscle" .)