Eg, proton (8)
I believe the answer is:
particle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">eg proton</span>' is the definition.<br/ ><span class="explanation-format__explanation">(proton is a type of subatomic particle)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for particle that I've seen before include "Grain, tiny piece" , "Speck of matter" , "Eg, a proton" , "Prelatic (anag.)" , "Tiny piece of anything" .)