e ‧ lec ‧ tron /ɪˈlektrɒn $ -trɑːn/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Origin: electro- + -on (as in ion) ]
a very small piece of matter with a negative electrical ↑ charge that moves around the ↑ nucleus (=central part) of an atom ⇨ proton , neutron