Breadcrumb Home > Dictionary > Index C carbon 12: Meaning and Definition of Find definitions for: carbon 12 Pronunciation: (kär'bun twelv'). [key] the isotopic carbon atom that comprises 99 percent of naturally occurring carbon, and that since 1961 has been used as the standard for atomic weight by representing a unit of 12.00000. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. carbon carbon 13 TrendingHere are the facts and trivia that people are buzzing about. The Book of Philippians: Summary Current Events This Week: May 2023 Preamble of the United Nations Charter Queen Victoria Books of the Bible: New Testament Books in Order The 88 Recognized Constellations ✖ Related Content Daily Word Quiz: panache Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language