Not one (4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not one</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 none that I've seen before include "Not any sort of neon" , "Pet menu chez Hubbard" , "service for monks" , "Not even one" , "Bugger all" .)
(Other definitions for neither that I've seen before include "Negative word" , "Not one thing or the other" , "Not one of two" , "The rein (anag.)" , "Also not" .)