Eighth letter of the Greek alphabet (5)
I believe the answer is:
theta
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">eighth letter of the greek alphabet</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 theta that I've seen before include "Greek letter used in trigonometry" , "Greek character" , "character from Greece" , "Homeric character" , "letter from Athens" .)