Test, investigation (10)
I believe the answer is:
experiment
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">test</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">investigation</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(experiment is a kind of investigation)</span><br/ ><br/ ></span>
(Other definitions for experiment that I've seen before include "Controlled test" , "scientific investigation" , "Trial" .)