pos ‧ i ‧ tron /ˈpɒzətrɒn, ˈpɒzɪtrɒn $ ˈpɑːzətrɑːn/ BrE AmE noun [countable] technical
[ Date: 1900-2000 ; Origin: positive + -tron (as in electron ) ]
a very small piece of matter that has the same mass as an ↑ electron but has a positive electrical ↑ charge