Molecule component (4)
I believe the answer is:
atom
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">molecule component</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for atom that I've seen before include "type of bomb" , "Not much substance" , "little amount" , "Smallest particle in an element able to take part in a chemical reaction" , "Very small object or amount" .)