atom

Meanings

1. 1
   noun

   the smallest component of an element having the chemical properties of the element

   Three oxygen atoms are found in the molecule ozone.

2. 2
   noun

   The smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons.

   Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis: the ability to convert water and carbon dioxide into carbohydrates and waste oxygen using solar energy. The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light. The critical component of the photosynthetic system is the water-oxidizing complex, made up of manganese atoms and a calcium atom.

3. 3
   noun

   The smallest, indivisible constituent part or unit of something.

   Towards the following morning, the thermometer fell to 5°; and at daylight, there was not an atom of water to be seen in any direction.

4. 4
   noun

   A very small amount; a whit.

   "Doctor, tell me one word more," said Theodore, quivering with suppressed emotion. "How do you think it will end?" / "I have hardly the faintest atom of hope," answered this honest, earnest man.

5. 5
   noun

   A non-zero member of a partially ordered set that has only zero below it (assuming that the poset has a least element, its "zero").

   In a Venn diagram, an atom is depicted as an area circumscribed by lines but not cut by any line.

6. 6
   noun

   (nontechnical usage) a tiny piece of anything

7. 7
   noun

   A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter.

8. 8
   noun

   In logical atomism, a fundamental fact that cannot be further broken down.

Etymology

From Middle English attome, from Middle French athome, from Latin atomus (“smallest particle”), from Ancient Greek ἄτομος (átomos, “indivisible”), from ἀ- (a-, “not”) + τέμνω (témnō, “to cut”, o-grade in τομ-) + -ος (-os). Atoms are so named because they were historically thought up as to be the smallest unit of matter, and thus indivisible. Doublet of atomus.