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atmosphere
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atom

at·om [ áttəm ] (plural at·oms)


noun 
Definition:
 
1. smallest part of element: the smallest portion into which an element can be divided and still retain its properties, made up of a dense, positively charged nucleus surrounded by a system of electrons. Atoms usually do not divide in chemical reactions except for some removal, transfer, or exchange of specific electrons.

2. very small amount: a very small part or amount
not an atom of truth

3. particle of matter in Greek philosophy: the basic particle of matter, indestructible and indivisible, first proposed by ancient Greek philosophers as the fundamental component of the universe

[16th century. < Latin atomus< Greek atomos "unable to be cut" < temnein "to cut"]
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