noun \ˈa-təm\

: the smallest particle of a substance that can exist by itself or be combined with other atoms to form a molecule

: a very small amount of something

Full Definition of ATOM

:  one of the minute indivisible particles of which according to ancient materialism the universe is composed
:  a tiny particle :  bit
:  the smallest particle of an element that can exist either alone or in combination
:  the atom considered as a source of vast potential energy

Examples of ATOM

  1. There is not an atom of truth to what he said.
  2. <give me just one atom of information about the novel's surprise ending>

Origin of ATOM

Middle English, from Latin atomus, from Greek atomos, from atomos indivisible, from a- + temnein to cut
First Known Use: 15th century

Other Physics Terms

amplitude, centrifugal, centripetal, convection, gradient, hysteresis, kinetic, lase, quantum


noun \ˈat-əm\   (Medical Dictionary)

Medical Definition of ATOM

: the smallest particle of an element that can exist either alone or in combination
atom·ic \ə-ˈtäm-ik\ adjective
atom·i·cal·ly \-i-k(ə-)lē\ adverb


noun    (Concise Encyclopedia)

The classical “planetary” model of an atom. The protons and neutrons in the nucleus are …—© Merriam-Webster Inc.

Smallest unit into which matter can be divided and still retain the characteristic properties of an element. The word derives from the Greek atomos (“indivisible”), and the atom was believed to be indivisible until the early 20th century, when electrons and the nucleus were discovered. It is now known that an atom has a positively charged nucleus that makes up more than 99.9% of the atom's mass but only about 1/100,000 of its volume. The nucleus is composed of positively charged protons and electrically neutral neutrons, each about 2,000 times as massive as an electron. Most of the atom's volume consists of a cloud of electrons that have very small mass and negative charge. The electron cloud is bound to the nucleus by the attraction of opposite charges. In a neutral atom, the protons in the nucleus are balanced by the electrons. An atom that has gained or lost electrons becomes negatively or positively charged and is called an ion.


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