at·om | \ ˈa-təm \

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

For more than a century, the origin of cosmic rays — fragments of atoms that rain down on the Earth at close to the speed of light — had been one of the great mysteries in science, thwarting the best minds in physics. Mark Johnson, Milwaukee Journal Sentinel, "Blazing a trail: UW professor's dream leads to breakthrough in identifying origin of cosmic rays," 12 July 2018 Enceladus has a subsurface ocean and shoots jets of water vapor that becomes ionized (stripped of some atoms) and wind up circling Saturn. Joe Pappalardo, Popular Mechanics, "Saturn and Its Moon Enceladus Talk To Each Other. The Sound Is Perfectly Cosmic and Eerie.," 10 July 2018 Now, scientists working with data from a dead spacecraft have discovered something even more potentially intriguing: heavy organic compounds containing hundreds of atoms arranged in rings and chains. National Geographic, "Right Stuff for Life Found on Small Saturn Moon," 27 June 2018 The potential split atom of our democracy forever threatens to be our annihilation. Michael Paterniti, GQ, "Jimmy Carter for Higher Office," 26 June 2018 The Cold Atom Laboratory (CAL) device is designed to help scientists study the strange behavior of atoms at ultra-low temperatures — in this case, 10 billion times colder than the frigid vacuum of space. Denise Chow /, NBC News, "Space station experiment will create the coldest spot in the universe," 22 June 2018 The spacecraft, which will be unmanned, will be loaded with 10 scientific instruments, including one that will provide imaging of the heliosphere and track the flow of interstellar neutral atoms, Schwadron said. Elise Takahama,, "NASA selects UNH researchers for mission to study safer space travel," 8 June 2018 The nucleus is a scary place for people like me, who prefer the gentler world of whole atoms and molecules. Chris Lee, Ars Technica, "Cloud-based quantum computer takes on deuteron and wins," 30 May 2018 Scientists have observed this phenomenon in tiny objects such as atoms and electrons. Gabriel Popkin, Science | AAAS, "Einstein’s ‘spooky action at a distance’ spotted in objects almost big enough to see," 25 Apr. 2018

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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Dictionary Entries near atom






atom beam


Statistics for atom

Last Updated

31 Aug 2018

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Time Traveler for atom

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

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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 \

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 \

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 \ adjective
atomically \-i-k(ə-)lē \ adverb

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More from Merriam-Webster on atom

Thesaurus: All synonyms and antonyms for atom

Spanish Central: Translation of atom

Nglish: Translation of atom for Spanish Speakers

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

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