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

These devices use quantum systems, such as atoms or electron spins, as highly sensitive probes. —Alex Krasnok, The Conversation, 19 June 2026

Separate laser systems can also move atoms around, providing any-to-any connectivity, which enables considerable flexibility for algorithmic and error-correction purposes. —ArsTechnica, 17 June 2026

Using the chemical reaction that occurs on the Sun, fusion energy can potentially generate large amounts of energy from simpler atoms like hydrogen and its isotopes. —Ameya Paleja, Interesting Engineering, 17 June 2026

So, just as red light, green light, and blue light blend to make white, so do red, blue, and green quarks form color-neutral protons and neutrons (the building blocks of atoms). —Quanta Magazine, 15 June 2026

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