at·​om | \ ˈa-təm How to pronounce atom (audio) \

Definition of atom

1a : the smallest particle of an element that can exist either alone or in combination an atom of hydrogen
b : the atom considered as a source of vast potential constructive or destructive energy … a largely forgotten legacy of this country's conquest of the atom.— William J. Broad … when Congress passed the Atomic Energy Act in 1954 and allowed private utilities to "harness the atom."— Barry Werth
2 : a tiny particle : bit There's not an atom of truth in what he said.
3 : one of the minute indivisible particles of which according to ancient materialism (see materialism sense 1a) the universe is composed

Did you know?

Some ancient philosophers believed that matter is infinitely divisible, that any particle, no matter how small, can always be divided into smaller particles. Others believed that there must be a limit and that everything in the universe must be made up of tiny indivisible particles. Such a hypothetical particle was called atomos in Greek, which means “indivisible.” According to modern atomic theory, all matter is made up of tiny particles named atoms from the ancient Greek atomos. However, it has turned out that atoms are not indivisible after all. Indeed, the splitting of atoms can be used to produce vast amounts of energy, as in atom bombs.

Examples of atom in a Sentence

There is not an atom of truth to what he said. give me just one atom of information about the novel's surprise ending
Recent Examples on the Web Per Deadline, Nolan's twelfth movie Oppenheimer focuses on theoretical physicist J. Robert Oppenheimer, who played a key role in the research process and development of the atom bomb during the 1940s. Emma Dibdin, Town & Country, 21 July 2022 That’s what a permanent magnet is — a bunch of little superconducting loops, one in each atom. Sumeet Kulkarni, Los Angeles Times, 2 July 2022 One such mechanism, called methylation, involves a methyl group—a methane molecule that is missing one of its four hydrogen atoms, leaving a chemical bond free to attach to another atom or molecule. Rachel Yehuda, Scientific American, 18 June 2022 This limit is essentially the atom’s actual oscillation. Joshua Hawkins, BGR, 18 July 2022 Rather than being emitted as electrons, a small fraction of the decaying atom’s energy had apparently vanished. Joanna Thompson, Scientific American, 15 June 2022 The wavelength that won the contest was designated as the natural resonance frequency of the atom. New York Times, 25 Apr. 2022 Currently, the ion-trap method uses a significant number of lasers to manipulate the ytterbium atom, which is something that is not sustainable long-term. Moneyshow, Forbes, 5 May 2021 Eventually the atom will settle down into a stable state, where the region around the missing electron is marked by a scar—a place where an electron should be but isn’t. Frank Wilczek, WSJ, 19 May 2022 See More

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

First Known Use of atom

15th century, in the meaning defined at sense 3

History and Etymology for atom

Middle English, from Latin atomus, from Greek atomos, from atomos indivisible, from a- + temnein to cut

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The first known use of atom was in the 15th century

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Last Updated

3 Aug 2022

Cite this Entry

“Atom.” Dictionary, Merriam-Webster, Accessed 14 Aug. 2022.

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More Definitions for atom


at·​om | \ ˈa-təm How to pronounce atom (audio) \

Kids Definition of atom

1 : the smallest particle of an element that can exist alone or in combination carbon atoms
2 : a tiny particle : bit "I don't believe there's an atom of meaning in it."— Lewis Carroll, Alice's Adventures in Wonderland


at·​om | \ ˈat-əm How to pronounce atom (audio) \

Medical Definition of atom

: the smallest particle of an element that can exist either alone or in combination

Other Words from atom

atomic \ ə-​ˈtäm-​ik How to pronounce atom (audio) \ adjective
atomically \ -​i-​k(ə-​)lē How to pronounce atom (audio) \ adverb

More from Merriam-Webster on atom

Nglish: Translation of atom for Spanish Speakers

Britannica English: Translation of atom for Arabic Speakers Encyclopedia article about atom


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