Relating to a duke (5)
I believe the answer is:
ducal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">relating to a duke</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 ducal that I've seen before include "of Wellington?" , "Representing noble" , "Relating to one level of nobility" , "Aristocratic" , "Pertaining to a duke" .)