Sternum (10)
I believe the answer is:
breastbone
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sternum</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for breastbone that I've seen before include "Rib neighbour" , "Sternum" .)