Imaginary monster (8)
I believe the answer is:
bogeyman
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">imaginary monster</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 bogeyman that I've seen before include "Children fear him - a bad golfer?" , "Imaginary monster to frighten children" , "Monster used to frighten children" , "Spectre terrifying to children" , "Person (real or imaginary) used as a threat to children" .)