Sexual desire (6)
I believe the answer is:
libido
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sexual desire</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that libido is a type of sexual desire)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for libido that I've seen before include "Sexual or psychological urge" , "Instinctive desire" , "lust!" , "Life force" , "Vital urge" .)