Tendons (6)
I believe the answer is:
sinews
'tendons' is the definition.
('sinew' can be a synonym of 'tendon')
This is all the clue.
(Other definitions for sinews that I've seen before include "They connect muscle to bone" , "Tissue connecting muscles to bones" , "Tough tissues joining muscles to bone" , "Tissues connecting muscles to bones" , "Power" .)