atom

noun

at·​om ˈa-təm 

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.

Synonyms of atom

• particle
• speck
• molecule
• fleck
• bit
• grain
• patch
• snippet
• scrap

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

In my favorite works of his, like A Case for the Existence of God and A Bright New Boise—a play that has its own surreal dynamic with television screens, which play images of hell in the middle of a big-box store—Hunter locates an unnerving mysticism in between the atoms of the hyper-real. —Jackson McHenry, Vulture, 31 Oct. 2025

The idea traces back to 2018, when former Stanford PhD student William Gent theorized that iron could be pushed to higher oxidation states if neighboring atoms were carefully spaced apart. —Neetika Walter, Interesting Engineering, 30 Oct. 2025

Fission splits the nuclei of atoms to create power while fusion causes hydrogen nuclei to collide and fuse into helium atoms that release incredible amounts of energy — essentially replicating the power of the sun. —Rob Nikolewski, San Diego Union-Tribune, 29 Oct. 2025

Fusion, the same reaction that powers the sun, makes energy via the opposite process of today’s nuclear power plants, joining light atoms rather than splitting heavier ones. —Harry Booth, Time, 29 Oct. 2025

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

Phrases Containing atom

• atom smasher

Rhymes for atom

• datum
• stratum
• erratum
• striatum
• substratum
• heteroatom
• petrolatum

Kids Definition

atom

noun

at·​om ˈat-əm 

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 

: the smallest particle of an element that can exist either alone or in combination

atomic

ə-ˈtäm-ik 

adjective

atomically

-i-k(ə-)lē 

adverb