Communication system (8)
I believe the answer is:
language
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">communication system</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 language that I've seen before include "Formalised system of communication" , "Irish, English, French, for instance" , "System of words used by a group" , "Tongue" , "talk" .)