Greek T
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">greek t</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 tau that I've seen before include "A subatomic particle" , "letter from foreigner" , "19th letter of the Greek alphabet" , "Foreign character" , "character from Athens" .)