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

Applying enough voltage to the device causes tiny regions in the dielectric layer—where oxygen atoms are missing—to form filaments that bridge the electrodes or otherwise move in a way that makes the layer more conductive. —Perri Thaler, IEEE Spectrum, 27 Nov. 2025

High-power microwave radiation energized the atoms of the gases into a hot plasma state, which freed up carbon atoms to settle on the wafers, and linked into the diamond structure over the course of several hours. —Abhimanyu Ghoshal, New Atlas, 27 Nov. 2025

Be thankful for the atoms and molecules that have assembled to make you. —Big Think, 27 Nov. 2025

The energy signature of these gamma-rays closely matches those predicted to emerge from the annihilation of colliding WIMPs, which are predicted to have a mass around 500 times that of a proton, the ordinary matter particles found at the heart of atoms. —Robert Lea, Space.com, 25 Nov. 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