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 Imagine suddenly plucking an electron out of an atom of material. Frank Wilczek, WSJ, 19 May 2022 Nuclear fusion is not to be confused with nuclear fission — the process that splits an atom and then can be used to generate electricity at nuclear power plants, such as the now-shuttered San Onofre Nuclear Generating Station. Rob Nikolewski, San Diego Union-Tribune, 17 Mar. 2022 But improving upon the cesium 133 atom comes with improvements in our laser capabilities. Tim Newcomb, Popular Mechanics, 26 Apr. 2022 Put simply, there is no vaccine, moonshot or atom bomb for alternative energy. WSJ, 26 Apr. 2022 The Nuclear Test Ban Treaty Organization has recorded more than 25 atom-bomb-scale asteroid impacts to Earth’s atmosphere since 2000, using a network of infrasound (very low frequency sound) sensors around the world. Manasee Wagh, Popular Mechanics, 26 Apr. 2022 But the force could also take any value in between, including zero if the atom’s north-south axis was horizontal. Davide Castelvecchi, Scientific American, 8 Feb. 2022 Every atom inside of your body was, at one point, part of a distant star. Clayton and the rest of us may not have the stuff to become captains of industry. Washington Post, 19 Nov. 2021 Military planners have worked to avoid a clash between the world's two biggest nuclear powers since the Soviet Union acquired its first atom bomb at the start of the Cold War. Arkansas Online, 20 Mar. 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

Buying Guide

Encourage future scientists with science kits selected by our Reviews team.

Learn More About atom

Time Traveler for atom

Time Traveler

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

See more words from the same century

Dictionary Entries Near atom




See More Nearby Entries 

Statistics for atom

Last Updated

23 May 2022

Cite this Entry

“Atom.” Dictionary, Merriam-Webster, Accessed 24 May. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

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


Test Your Vocabulary

Name That Food

  • a-light
  • Name these cookies!
True or False

Test your knowledge - and maybe learn something along the way.

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!