pionPronunciation: /ˈpʌɪɒn/Definition of pion noun Physics a meson having a mass approximately 270 times that of an electron. Also called pi-meson.Derivatives pionicPronunciation: /pʌɪˈɒnɪk/ adjective Origin: 1950s: from pi1 (the letter used as a symbol for the particle) + -onpion in other Oxford dictionaries Definition of pion in the US English dictionary
