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. Biographies: Notable Jewish Religious Leaders Current Events This Week: September 2023 Hispanic Population and the 2010 U.S. Census Preamble of the United Nations Charter The Jewish Calendar ✖ Related Content Daily Word Quiz: bildungsroman Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language