Completely, entirely (5)
I believe the answer is:
fully
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">completely</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(in full)</span><br/ ><br/ >'<span class="explanation-format__original">entirely</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for fully that I've seen before include "Wholly" , "Completely" , "Entirely" , "In all respects" .)