Young racehorse (8)
I believe the answer is:
yearling
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">young racehorse</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for yearling that I've seen before include "Animal between 1 and 2 in age" , "Sort of racehorse" , "A racehorse under 2" , "Young horse" , "Relaying (anag.)" .)