Trident-shaped Greek letters (4)
I believe the answer is:
psis
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">trident-shaped greek letters</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 psis that I've seen before include "letters from abroad" , "letters from Greece" .)