Original idea (10)
I believe the answer is:
brainchild
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">original idea</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 brainchild that I've seen before include "One's original idea" , "Original idea or work" , "Invention" , "wheeze" , "Bright idea" .)