a short-lived atomic system consisting of a positron and an electron bound together.
Origin of positronium
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
physics a short-lived entity consisting of a positron and an electron bound together. It decays by annihilation to produce two or three photons
Word Origin for positronium
C20: from positron + -ium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012