Medical Dictionary

atom at·om (āt'əm)

  1. A unit of matter, the smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons. The entire structure has an approximate diameter of 10-8 centimeter and characteristically remains undivided in chemical reactions except for limited removal, transfer, or exchange of certain electrons.

  2. This unit regarded as a source of nuclear energy.

  3. A part or particle considered to be an irreducible constituent of a specified system.

  4. The irreducible, indestructible material unit postulated by ancient atomism.

  5. An extremely small part, quantity, or amount.

a·tom'ic (ə-tŏm'ĭk) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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