A negatively charged particle (8)
I believe the answer is:
electron
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a negatively charged particle</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 electron that I've seen before include "In small part" , "Elementary particle with negative charge" , "Particle found in all atoms" , "Charged subatomic particle" , "Negatively charged particle" .)