Baseless rumour (6)
I believe the answer is:
canard
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">baseless rumour</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 canard that I've seen before include "A French kind of false rumour" , "A false rumour, originally French" , "'False report, hoax (6)'" , "Deliberately misleading fabrication" , "Ugly rumour" .)