/ Dictionary / Index P pyrimethamine: Meaning and Definition of Find definitions for: py•ri•meth•a•mine Pronunciation: (pī"ru-meth'u-mēn", -min), [key] — n. Pharm. a potent substance, CHClN, used against susceptible plasmodia in the prophylactic treatment of malaria and against Toxoplasma gondi in the treatment of toxoplasmosis. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. pyriform pyrimidine Related Content Daily Word Quiz: fervor Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language