/ Dictionary / Index P prototherian: Meaning and Definition of Find definitions for: pro•to•the•ri•an Pronunciation: (prō"tu-thēr'ē-un), [key] — adj. belonging or pertaining to the group Prototheria, comprising the monotremes. —n. a prototherian animal. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: prototherian (Thesaurus) protostome prototroph Related Content Daily Word Quiz: feline Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language