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

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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 To be fervently pro-nuclear, in the manner of Hoff and Zaitz, is to see in the peaceful splitting of the atom something almost miraculous. Rebecca Tuhus-dubrow, The New Yorker, "The Activists Who Embrace Nuclear Power," 19 Feb. 2021 In a speech to the United Nations General Assembly, President Dwight D. Eisenhower asks the world’s major powers to work together in developing peacetime uses of the atom. Cnn Editorial Research, CNN, "Nuclear Power/IAEA Fast Facts," 13 Apr. 2021 These science and healthcare listmakers are inventing the future from the atom up. Leah Rosenbaum, Forbes, "30 Under 30 Europe 2021: Changing The World From Artificial Intelligence To Covid-19," 8 Apr. 2021 The muon is the heavier cousin to the electron that orbits an atom's center. Seth Borenstein, Star Tribune, "'Tantalizing' results of 2 experiments defy physics rulebook," 7 Apr. 2021 As a result, these relatively untethered particles are free to move around, hopping from one atom to another, and forming the basis for electricity. Miriam Fauzia, USA TODAY, "Fact check: Bending an electrical wire won't stop flow of electricity," 6 Apr. 2021 Hydrogen is a really small atom and easily gets through microscopic pores, even biological membranes and cell walls. James Conca, Forbes, "Japan Will Release Radioactive Fukushima Water Into The Ocean," 12 Apr. 2021 Rabi, a Nobel laureate who helped America develop the atom bomb, was reflecting physicists’ general surprise that muons, which are, to all intents and purposes, just heavy and unstable versions of electrons, actually exist. The Economist, "Particle physics A second possible break in the laws of physics has been noted," 7 Apr. 2021 Godzilla served as a terrifying symbol for the atom bomb. Keith Phipps, Vulture, "All 15 Classic Godzilla Movies, Ranked," 31 Mar. 2021

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.

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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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Time Traveler for atom

Time Traveler

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

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Statistics for atom

Last Updated

11 May 2021

Cite this Entry

“Atom.” Dictionary, Merriam-Webster, Accessed 14 May. 2021.

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More Definitions for atom



English Language Learners Definition of atom

: the smallest particle of a substance that can exist by itself or be combined with other atoms to form a molecule
: a very small amount of something


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

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