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]

WordNet (r) 3.0 (2006):

unitary
    adj 1: relating to or characterized by or aiming toward unity;
           "the unitary principles of nationalism"; "a unitary
           movement in politics"
    2: of or pertaining to or involving the use of units; "a unitary
       method was applied"; "established a unitary distance on which
       to base subsequent calculations"
    3: characterized by or constituting a form of government in
       which power is held by one central authority; "a unitary as
       opposed to a federal form of government" [ant: federal]
    4: having the indivisible character of a unit; "a unitary
       action"; "spoke with one voice" [syn: one(a), unitary]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "unitary":
   a certain, an, any, any one, atomic, composite, either, exclusive,
   individual, indivisible, integral, integrant, integrated,
   irreducible, lone, monadic, monistic, one, rolled into one, simple,
   single, singular, sole, solid, solitary, unanalyzable, undivided,
   unified, uniform, unique, united, whole