Long-tailed primate (6)
I believe the answer is:
monkey
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">long-tailed primate</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 monkey that I've seen before include "Five hundred pounds (colloq.); imp" , "Primate with a long tail" , "Araucaria -- evergreen conifer" , "Any of various long-tailed primates" , "Primate; five hundred (slang)" .)