carbon 12

noun (1)

Definition of carbon 12

 (Entry 1 of 4)

: an isotope of carbon of mass number 12 that is the most abundant carbon isotope and is used as a standard for measurements of atomic weight


\ ˈtwelv-ˌstep How to pronounce 12-step (audio) \

Definition of 12-step (Entry 2 of 4)

: of, relating to, characteristic of, or being a program that is designed especially to help an individual overcome an addiction, compulsion, serious shortcoming, or traumatic experience by adherence to 12 tenets emphasizing personal growth and dependence on a higher spiritual being

12 a.m.

noun (2)

Definition of 12 a.m. (Entry 3 of 4)

: midnight : one hour after 11 p.m.

12 p.m.

noun (3)

Definition of 12 p.m. (Entry 4 of 4)

: one hour after 11 a.m. : noon

Examples of carbon 12 in a Sentence

Recent Examples on the Web: Noun

The key is in the rock’s atomic composition; organisms that use sunlight for energy incorporate a lighter version of carbon, called carbon 12, over the heavier carbon 13. Peter Byrne, Quanta Magazine, "Early Life in Death Valley," 24 Apr. 2014

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'carbon 12.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of carbon 12

Noun (1)

1936, in the meaning defined above


1983, in the meaning defined above

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Statistics for carbon 12

Last Updated

23 Jun 2019

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Time Traveler for carbon 12

The first known use of carbon 12 was in 1936

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Comments on carbon 12

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to complain fretfully

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