Flabbergast, greatly surprise (7)
I believe the answer is:
astound
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">flabbergast</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">greatly surprise</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for astound that I've seen before include "Startle" , "Shock, surprise greatly" , "Stagger" , "Shock - amaze" , "Stupefy" .)