Tendon (5)
I believe the answer is:
sinew
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tendon</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sinew that I've seen before include "Force" , "Tough connective tissue" , "Inelastic tissue" , "As synonym for 'strength'" , "source of physical strength" .)