atom

Short definition from Wiktionary

Noun

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

Proper noun

1. 1
   A Meitei surname from Manipuri