Second Greek letter (4)
I believe the answer is:
beta
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">second 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 beta that I've seen before include "second class grade?" , "Second letter of the Greek alphabet" , "less than perfect mark" , "In a constellation, a star second in brightness" , "Old character" .)