Dictionary (7)
I believe the answer is:
lexicon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dictionary</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lexicon that I've seen before include "it has a lot of words" , "Dictionary of terms" , "reference work?" , "Nice lox (anag)" , "Wordbook" .)