Fountainhead (6)
I believe the answer is:
source
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fountainhead</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for source that I've seen before include "Origin; spring" , "Where something originates" , "Place or person where something begins" , "Beginning to add" , "Origin; head of stream" .)