/ Dictionary / Index P proton number: Meaning and Definition of Find definitions for: pro'ton num"ber. Pronunciation: [key] See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. protonema protonotary Related Content Daily Word Quiz: knead Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language