pro ‧ ton /ˈprəʊtɒn $ ˈproʊtɑːn/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Language: Greek ; Origin: 'first thing' , from protos ; ⇨ ↑ proto- ]
a very small piece of matter with a positive electrical ↑ charge that is in the central part of an atom ⇨ electron , neutron