The Collaborative International Dictionary of English v.0.48:

Atomistic \At`om*is"tic\, a.
   1. Of or pertaining to atoms; relating to atomism. [R.]
      [1913 Webster]

            It is the object of the mechanical atomistic
            philosophy to confound synthesis with synartesis.
                                                  --Coleridge.
      [1913 Webster]

   2. divided into separate and often disparate elements; -- the
      opposite of holistic.

   Syn: atomistical.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

atomistic
    adj 1: divided into separate and often disparate elements [syn:
           atomistic, atomistical] [ant: holistic]