Definition of “atom” - English Dictionary

british dictionary

“atom” in British English

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atomnoun [ C ]

uk /ˈæt.əm/ us /ˈæt̬.əm/

B2 the smallest unit of any chemical element, consisting of a positive nucleus surrounded by negative electrons. Atoms can combine to form a molecule:

A molecule of carbon dioxide (CO2) has one carbon atom and two oxygen atoms.
figurative He hasn't an atom of sense (= he has no sense), that boy.

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(Definition of “atom” from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

“atom” in American English

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atomnoun [ C ]

us /ˈæt̬·əm/

physics the smallest unit of any chemical element, consisting of a positive nucleus surrounded by negative electrons. Atoms can combine to form a molecule.

(Definition of “atom” from the Cambridge Academic Content Dictionary © Cambridge University Press)