Particle in an electrolyte (3)
I believe the answer is:
ion
'particle in an electrolyte' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ion that I've seen before include "Electrically-charged particle" , "Particle (phys.)" , "Eletrically charged particle" , "Charged atom/molecule" , "Electrically charged particle" .)