/ Dictionary / Index X xi particle: Meaning and Definition of Find definitions for: xi' par"ticle Pronunciation: [key] — Physics. Physics. any of a family of baryons having strangeness −2 and isotopic spin . Symbol: &Xgr; Cf. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. -xion Xipe Related Content Daily Word Quiz: inutiae Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language