atomic

Short definition from Wiktionary

Adjective

1. 1
   Of or relating to atoms; composed of atoms; monatomic.
2. 2
   Employing or relating to nuclear energy or processes.
3. 3
   Employing or relating to nuclear energy or processes: Very strong and overpowering.
4. 4
   Infinitesimally small.
5. 5
   Unable to be split or made any smaller.
6. 6
   Unable to be split or made any smaller: Containing a single change, as opposed to involving numerous unrelated changes.
7. 7
   Unable to be split or made any smaller: Lacking logical operators; unable to be made simpler in logical form.
8. 8
   Unable to be split or made any smaller: Such that for every element b>0 there exists an atom a such that b≥a>0.
9. 9
   Guaranteed to complete either fully or not at all while waiting in a pause, and running synchronously when called by multiple asynchronous threads.

Noun

1. 1
   An atomic operation.