Disappointed (3,4)
I believe the answer is:
let down
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">disappointed</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for let down that I've seen before include "Disappoint or fail - or lengthen garment" , "Failed - deflated" , "Disappoint, fail to support" , "Disappoint, fail to keep promise" , "Aircraft descent" .)