Dictionary
pi•on
Pronunciation: (pī'on), [key]—
n. Physics.
the first meson to be discovered: it has spin 0 and may be positively or negatively charged or neutral; charged pions decay into a muon and a neutrino or antineutrino.
Symbol: π Also called
pi meson. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.