/ Dictionary / Index P petrogenesis: Meaning and Definition of Find definitions for: pet•ro•gen•e•sis Pronunciation: (pe"trō-jen'u-sis), [key] — n. the branch of petrology dealing with the origin and formation of rocks. the origin and formation of rocks. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. petrog. petroglyph 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