Run quickly (4)
I believe the answer is:
hare
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">run quickly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(hare can mean to run fast)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for hare that I've seen before include "Leveret" , "Fast-running mammal" , "As mad as this March animal" , "'You can't run with the . . . . and hunt with the hounds'" , "Mammal - run fast" .)