/ Dictionary / Index P prosternum: Meaning and Definition of Find definitions for: pro•ster•num Pronunciation: (prō-stûr'num), [key] — pl. -na -nums. the ventral sclerite of the prothorax of an insect. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. prostatitis prosthesis Related Content Daily Word Quiz: mamba Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language