Meaning of psi particle

psi' par"ticle

Pronunciation: (sī, psī), [key]
— Physics. Physics.
  1. any of a family of mesons consisting of a charmed quark and a charmed antiquark.
  2. an early name for the J/psi particle.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.