/ Dictionary / Index P protonema: Meaning and Definition of Find definitions for: pro•to•ne•ma Pronunciation: (prō"tu-nē'mu), [key] — pl. -ma•ta a primary, usually filamentous structure produced by the germination of the spore in mosses and certain related plants, and from which the leafy plant which bears the sexual organs arises as a lateral or terminal shoot. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. proton proton number 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