atom

noun12

1. •
   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.
2. •
   A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter.
3. •
   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. — 1835
4. •
   In logical atomism, a fundamental fact that cannot be further broken down.
5. •
   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. — 1873
6. •
   An individual number or symbol, as opposed to a list; a scalar value.
7. •
   An element of a set that is not itself a set; an urelement.
8. •
   [before a noun] (Canada) An age group division in hockey for nine- to eleven-year-olds.
9. •
   A mote of dust in a sunbeam.
10. •
    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.
11. •
    An integer representing a particular string.
12. •
    (historical) The smallest medieval unit of time, equal to fifteen ninety-fourths of a second.