Move very fast (6)
I believe the answer is:
streak
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">move very fast</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 streak that I've seen before include "Long mark, run swiftly" , "Unbroken series, of luck say" , "Move very fast; thin strip" , "Long thin mark" , "Run naked in a public place" .)