/ Dictionary / Index P prostoon: Meaning and Definition of Find definitions for: pro•sto•on Pronunciation: (prō-stō'on), [key] — pl. -sto•a (in classical architecture) a portico. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. prostomium prostrate Related Content Daily Word Quiz: careening Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language