Solar wind particle (3)
I believe the answer is:
ion
'solar wind particle' 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 "Charged atom/molecule" , "Electrically charged atom or group of atoms" , "Eletrically charged particle" , "Electrically charged particle" , "Particle (phys.)" .)