Set of letters (8)
I believe the answer is:
alphabet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">set of letters</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for alphabet that I've seen before include "A-Z" , "A to Z inclusive" , "Confusing assortment of initials" , "Whole set of letters" , "Ordered set of letters" .)