Vicious dog (3)
I believe the answer is:
cur
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">vicious dog</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 cur that I've seen before include "Inferior dog or one of mixed breed" , "Mongrel - coward" , "A worthless dog or contemptible person" , "Non-pedigree dog" , "Lowly dog" .)