Tissue attaching muscle to bone (6)
I believe the answer is:
tendon
'tissue attaching muscle to bone' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tendon that I've seen before include "Muscle-bone link" , "Ligament - sinew" , "Strong cord of tissue connecting muscle" , "Fibrous band" , "Tissue connecting a muscle with its bony attachment" .)