Obnoxious (6)
I believe the answer is:
odious
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">obnoxious</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 odious that I've seen before include "Detestable, execrable" , "Loathsome and repulsive" , "Replusive, abhorrent (6)" , "Comparisons are said to be thus" , "Unequivocally detestable" .)