/ Dictionary / Index P protostar: Meaning and Definition of Find definitions for: pro•to•star Pronunciation: (prō'tō-stär"), [key] — n. Astron. an early stage in the evolution of a star, after the beginning of the collapse of the gas cloud from which it is formed, but before sufficient contraction has occurred to permit initiation of nuclear reactions at its core. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. protopresbyter protostele Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language