To's counterpart (3)
I believe the answer is:
fro
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">to's counterpart</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for fro that I've seen before include "Opposite direction to to" , "To and - means back and forth" .)