Source : Webster's Revised Unabridged Dictionary (1913)

Atomic \A*tom"ic\, Atomical \A*tom"ic*al\, a. [Cf. F. atomique.]
   1. Of or pertaining to atoms.

   2. Extremely minute; tiny.

   {Atomic philosophy}, or {Doctrine of atoms}, a system which,
      assuming that atoms are endued with gravity and motion,
      accounted thus for the origin and formation of all things.
      This philosophy was first broached by Leucippus, was
      developed by Democritus, and afterward improved by
      Epicurus, and hence is sometimes denominated the Epicurean
      philosophy.

   {Atomic theory}, or the {Doctrine of definite proportions}
      (Chem.), teaches that chemical combinations take place
      between the supposed ultimate particles or atoms of
      bodies, in some simple ratio, as of one to one, two to
      three, or some other, always expressible in whole numbers.
      

   {Atomic weight} (Chem.), the weight of the atom of an element
      as compared with the weight of the atom of hydrogen, taken
      as a standard.

Source : WordNet®

atomic
     adj 1: of or relating to or comprising atoms; "atomic structure";
            "atomic hydrogen"
     2: (weapons) deriving destructive energy from  the release of
        atomic energy; "nuclear war"; "nuclear weapons"; "atomic
        bombs" [syn: {nuclear}] [ant: {conventional}]
     3: immeasurably small [syn: {atomlike}, {minute}]

Source : Free On-Line Dictionary of Computing

atomic
     
         (From Greek "atomos", indivisible) Indivisible;
        cannot be split up.
     
        For example, an instruction may be said to do several things
        "atomically", i.e. all the things are done immediately, and
        there is no chance of the instruction being half-completed or
        of another being interspersed.  Used especially to convey that
        an operation cannot be interrupted.
     
        An atomic {data type} has no internal structure visible to the
        program.  It can be represented by a flat {domain} (all
        elements are equally defined).  Machine {integers} and
        {Booleans} are two examples.
     
        An atomic {database transaction} is one which is guaranteed to
        complete successfully or not at all.  If an error prevents a
        partially-performed transaction from proceeding to completion,
        it must be "backed out" to prevent the database being left in
        an inconsistent state.
     
        [{Jargon File}]
     
        (2000-04-03)