2nd Greek letter (4)
I believe the answer is:
beta
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">2nd 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" , "software under test" , "second class grade?" , "In a constellation, a star second in brightness" , "It's next after alpha" .)