Track or follow (4)
I believe the answer is:
tail
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">track</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that track can be written as tail)</span><br/ ><br/ >'<span class="explanation-format__original">follow</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(both can mean to chase or pursue)</span><br/ ><br/ ></span>
(Other definitions for tail that I've seen before include "bum" , "Back end; follow secretly" , "Elongated posterior part of an animal" , "Queue" , "Hindmost part" .)