It carries a small charge (3)
I believe the answer is:
ion
'it carries a small charge' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ion that I've seen before include "Electrically-charged particle" , "Particle (phys.)" , "Electrically charged atom or group of atoms" , "Eletrically charged particle" , "Charged atom/molecule" .)