/ Dictionary / Index P prothalamium: Meaning and Definition of Find definitions for: pro•tha•la•mi•um Pronunciation: (prō"thu-lā'mē-um), [key] — pl. -mi•a prothalamion. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: prothalamium (Thesaurus) prothalamion prothallium Related Content Daily Word Quiz: rustic Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language