atom

noun

at·​om ˈa-təm How to pronounce atom (audio)
1
a
: 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 Lunar refineries could separate the hydrogen and oxygen atoms of water molecules, then possibly use them to create breathable air and rocket fuel—resources that are enormously expensive to send from Earth. David W. Brown, The New Yorker, 4 Mar. 2024 That leads to electromigration, a phenomenon where current in very narrow interconnects literally blows metal atoms out of place, leading to voids and open circuits. IEEE Spectrum, 28 Feb. 2024 Around the same time, physicists with labs specializing in manipulating cold atoms were confirming that real particles behaved in much the same way that digital ones did. Charlie Wood, Quanta Magazine, 26 Feb. 2024 At this point, a single atom of oxygen could mingle with two hydrogen atoms to form a molecule of water—a molecule that could, in a cosmic cycle of creation and destruction, still be sundered anew by high-energy radiation from stars and other astrophysical sources. Shannon Hall, Scientific American, 23 Feb. 2024 Rydberg atoms have also been used in astrophysics research. Paul Smith-Goodson, Forbes, 20 Feb. 2024 In that span, heat and pressure arrange the carbon’s atoms in a crystal structure that lends the resulting rocks their strength and sparkle. Amanda Mull, The Atlantic, 7 Feb. 2024 To understand Smith’s advice about escaping atoms, know that radon gas is radioactive. Bill Laytner, Detroit Free Press, 6 Feb. 2024 Most members of the filmmaking crew tell THR that the atom sequences were the most challenging on the film. Beatrice Verhoeven, The Hollywood Reporter, 11 Jan. 2024

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'atom.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

Etymology

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

First Known Use

15th century, in the meaning defined at sense 3

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

Dictionary Entries Near atom

Cite this Entry

“Atom.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/atom. Accessed 28 Mar. 2024.

Kids Definition

atom

noun
at·​om ˈat-əm How to pronounce atom (audio)
1
: a tiny particle : bit
2
: the smallest particle of an element that has the properties of the element and can exist either alone or in combination
3
: the atom considered as a source of vast potential energy
Etymology

Middle English atom "particle," from Latin atomus (same meaning), derived from Greek atomos "unable to be divided," from a- "not" and temnein "to cut"

Medical Definition

atom

noun
at·​om ˈat-əm How to pronounce atom (audio)
: the smallest particle of an element that can exist either alone or in combination
atomic adjective
atomically adverb

More from Merriam-Webster on atom

Last Updated: - Updated example sentences
Love words? Need even more definitions?

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