Working model (4-2)
I believe the answer is:
mock-up
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">working model</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 mock-up that I've seen before include "Dummy model" , "Model for testing purposes - sounds derisory" , "Full-scale model built for experimental purposes" , "Full-size working model" , "A model of something, sounds derisory" .)