atom

American  

[at-uhm] / ˈæt əm /

noun

1. Physics.

   1. the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.

   2. an atom with one of the electrons replaced by some other particle.

      muonic atom;

      kaonic atom.

2. Energy. this component as the source of nuclear energy.

3. a hypothetical particle of matter so minute as to admit of no division.

4. anything extremely small; a minute quantity.

   Synonyms:

   whit, jot, iota, scintilla, speck, shred

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atom British  

/ ˈætəm /

noun

1. 1. the smallest quantity of an element that can take part in a chemical reaction

   2. this entity as a source of nuclear energy See also atomic structure

      the power of the atom

2. any entity regarded as the indivisible building block of a theory

3. the hypothetical indivisible particle of matter postulated by certain ancient philosophers as the fundamental constituent of matter See also atomism

4. a very small amount or quantity; minute fragment

   to smash something to atoms

   there is not an atom of truth in his allegations

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atom Scientific  

/ ăt′əm /

1. The smallest unit of an element, consisting of at least one proton and (for all elements except hydrogen) one or more neutrons in a dense central nucleus, surrounded by one or more shells of electrons. In electrically neutral atoms, the number of protons equals the number of electrons. Atoms remain intact in chemical reactions except for the removal, transfer, or exchange of certain electrons.

2. Compare compound See also ion isotope orbital

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atom Cultural  

1. A unit of matter; the smallest unit of a chemical element. Each atom consists of a nucleus, which has a positive charge, and a set of electrons that move around the nucleus. (See Bohr atom.)

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Discover More

Atoms link together to form molecules.

Etymology

Origin of atom

First recorded in 1350–1400; Middle English attomos, athomus, from Latin atomus, from Greek átomos, noun use of átomos “undivided,” equivalent to a- a- ⁶ + tomós “divided,” from témnein “to cut”

Example Sentences

Oxygen atoms glow green and nitrogen light up in reds, blues and pinks.

From BBC

In this catalyst, each individual indium atom acts as its own active site.

From Science Daily

Through the years he took his stopped watches to “the One who set the atoms dancing,” or “who keeps the great currents circling through the sea.”

From Literature

It pulses more than a trillion times per second, closely matching the natural vibrations of atoms and electrons within materials.

From Science Daily

All the matter around us -- including the protons and neutrons that make up the nucleus of atoms -- are made of baryons.

From Barron's