Like lightning (4)
I believe the answer is:
fast
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">like lightning</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for fast that I've seen before include "Rapidly -- dissipated" , "Rapid - diet" , "Dissolute" , "Unlikely to run" , "Exercise for spiritual wellbeing" .)