Unit of language (4)
I believe the answer is:
word
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unit of language</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 word that I've seen before include "See 1" , "See 21" , "Message" , "Communication; news" , "Puzzle with solutions reading the same down as across" .)