Eighth Greek letter (5)
I believe the answer is:
theta
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">eighth greek letter</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for theta that I've seen before include "Greek letter equivalent to th" , "Foreign character" , "letter to Greeks" , "Make amends for" , "Letter to the Corinthians" .)