Of the backbone (6)
I believe the answer is:
spinal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">of the backbone</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for spinal that I've seen before include "of a vital column" , "affecting the back?" , "Member of dock family with edible stems" , "Type of column" , "Plains (anag.)" .)