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 Every atom and molecule has a unique spectrum, absorbing and emitting very particular shades of light. Sarah Scoles, Wired, "‘Dr. Phosphine’ and the Possibility of Life on Venus," 14 Sep. 2020 For context, the atom bomb dropped on Hiroshima 75 years ago had a yield of about 15 kilotons. Jonathan M. Gitlin, Ars Technica, "What we know about the massive chemical explosion in Beirut," 5 Aug. 2020 The team first simulated a simplified version of the energy state of a molecule consisting of 12 hydrogen atoms, with each of the 12 qubits representing one atom’s single electron. Neil Savage, Scientific American, "Google’s Quantum Computer Achieves Chemistry Milestone," 4 Sep. 2020 By just about any quantifiable metric, this was a firecracker vs. an atom bomb—and yet Dort was so nearly the hero, while Harden added yet another lackluster playoff performance to a pile that may one day eclipse all those accolades. Joe Freeman, oregonlive, "Trail Blazers’ biggest offseason question, Nets hire Steven Nash, Chris Paul alters Thunder road map, draft buzz: NBA playoffs news and notes," 3 Sep. 2020 Take his fellow physicist Erwin Schrödinger’s famous thought experiment in which a cat is trapped in a box with poison that will be released if a radioactive atom decays. Zeeya Merali, Scientific American, "This Twist on Schrödinger’s Cat Paradox Has Major Implications for Quantum Theory," 17 Aug. 2020 Celsius rips away an oxygen atom from each incoming CO2. Max G. Levy, Smithsonian Magazine, "To Make Oxygen on Mars, NASA’s Perseverance Rover Needs MOXIE," 29 July 2020 The condensate is key to applications like quantum computing and atom lasers. Caroline Delbert, Popular Mechanics, "A Physicist Made the Fifth State of Matter at Home, but at Least You Wore Pants Today," 27 May 2020 The Beirut fireball’s vivid red color sets it apart from the aftereffects of an atom bomb, too. Popular Science, "Why the Beirut blast created a mushroom cloud," 7 Aug. 2020

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

19 Sep 2020

Cite this Entry

“Atom.” Dictionary, Merriam-Webster, Accessed 22 Sep. 2020.

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More Definitions for atom


How to pronounce atom (audio)

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

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