Relating to motion (7)
I believe the answer is:
kinetic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">relating to motion</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for kinetic that I've seen before include "Like a mobile" , "(E.g. energy) of motion" , "Caused by motion" , "Relating to motion" , "due to motion" .)