Letter before beta (5)
I believe the answer is:
alpha
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">letter before beta</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for alpha that I've seen before include "European character" , "letter opener" , "best score" , "very good rating" , "First (class)" .)