Tooth's partner (4)
I believe the answer is:
nail
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tooth's partner</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 nail that I've seen before include "'For want of a . . . . the shoe was lost'" , "Brad, say" , "Hit this on the head to be dead right" , "A small steel wood pin" , "Metal fastener" .)