The Collaborative International Dictionary of English v.0.48:

Unitary \U"nit*a*ry\, a.
   1. Of or pertaining to a unit or units; relating to unity;
      as, the unitary method in arithmetic.
      [1913 Webster]

   2. Of the nature of a unit; not divided; united.
      [1913 Webster]

   Unitary theory (Chem.), the modern theory that the
      molecules of all complete compounds are units, whose parts
      are bound together in definite structure, with mutual and
      reciprocal influence on each other, and are not mere
      aggregations of more or less complex groups; --
      distinguished from the dualistic theory.
      [1913 Webster]