Allusion (9)
I believe the answer is:
reference
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">allusion</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 reference that I've seen before include "Book in which to find authoritative facts" , "Testimonial - allusion" , "Relation" , "Short note showing the source of information" , "Respect" .)