At full gallop (5)
I believe the answer is:
apace
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">at full gallop</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 apace that I've seen before include "fast" , "flat out" , "Swiftly, quickly" , "at high speed" , "(Move on) swiftly" .)