The Collaborative International Dictionary of English v.0.48:

concentrated \concentrated\ adj.
   1. Having a high density of (the indicated substance); as, a
      narrow thread of concentrated ore.

   Note: [Narrower terms: undiluted (vs. diluted)]
         [WordNet 1.5]

   2. Gathered together or made less diffuse; as, their
      concentrated efforts; his concentrated attention. Opposite
      of distributed or diffused.

   Note: [Narrower terms: bunched, bunchy, clustered;
         centered, centred, centralized, focused;
         undivided] [Also See: compact.]
         [WordNet 1.5]

   3. Intense; in an extreme degree; -- of mental phenomena; as,
      her concentrated passion held them at bay.
      [WordNet 1.5]

   4. being the most concentrated solution possible at a given
      temperature; unable to dissolve still more of a substance.
      Opposite of dilute or unsaturated.

   Note: [Narrower terms: supersaturated]

   Syn: saturated.
        [WordNet 1.5]

   5. reduced to a stronger or more concentrated form; as,
      concentrated sulfuric acid. Opposite of diluted.

   Syn: condensed.
        [WordNet 1.5]

   6. characterized by intensity; especially when imposed from
      without; -- of actions; as, concentrated study.

   Syn: intensive.
        [WordNet 1.5]

   7. characterized by mental concentration.

   Syn: intent.
        [WordNet 1.5 +PJC]

The Collaborative International Dictionary of English v.0.48:

Undiluted \Undiluted\
   See diluted.

WordNet (r) 3.0 (2006):

undiluted
    adj 1: not diluted; "undiluted milk"; "an undiluted racial
           strain" [ant: dilute, diluted]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "undiluted":
   absolute, bare, clarified, clear, distilled, naked, neat, perfect,
   plain, pure, purified, rectified, sheer, simple, straight,
   unadulterated, unalloyed, unblended, uncombined, uncompounded,
   uncorrupted, uncut, unfortified, unleavened, unmingled,
   unmitigated, unmixed, unqualified, unsophisticated, untinged,
   unwatered