/ Dictionary / Index P protonotary: Meaning and Definition of Find definitions for: pro•ton•o•tar•y Pronunciation: (prō-ton'u-ter"ē, prōt"n-ō'tu-rē), [key] — pl. -tar•ies. prothonotary. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. proton number proton-proton chain Related Content Daily Word Quiz: cosmology Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language