Frantically busy (6)
I believe the answer is:
hectic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">frantically busy</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 hectic that I've seen before include "Involving feverish activity, flushed" , "'Rushed, madly busy (6)'" , "Involving feverish activity, chaotic" , "particularly busy" , "Frantic or feverish" .)