Secretory organ (5)
I believe the answer is:
gland
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">secretory organ</span>' is the definition.<br/ ><span class="explanation-format__explanation">(gland is a kind of secretory organ)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for gland that I've seen before include "Organ secreting chemical substances" , "Organ that secretes" , "Organ that releases essential substances into the bloodstream" , "liver, for example" , "it could be described as secretive" .)