Green prefix (3)
I believe the answer is:
eco
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">green prefix</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 eco that I've seen before include "Umberto --, Italian writer" , "Green prefix" , "Umberto - - , novelist" , "Environmental group" , "Umberto -, Italian author (The Name of the Rose)" .)