/ Dictionary / Index P psi particle: Meaning and Definition of Find definitions for: psi' par"ticle Pronunciation: (sī, psī), [key] — Physics. Physics. any of a family of mesons consisting of a charmed quark and a charmed antiquark. an early name for the J/psi particle. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. psilosis psittacine Related Content Daily Word Quiz: careening Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language