Pretentiously impressive (9)
I believe the answer is:
grandiose
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pretentiously impressive</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 grandiose that I've seen before include "affected" , "Ridiculously impressive or imposing" , "Impressive in style" , "I grade son as affectedly splendid" , "Impressive, magnificent" .)