The Collaborative International Dictionary of English v.0.48:

Concentrate \Con*cen"trate\ (? or ?), v. t. [imp. & p. p.
   Concentrated; p. pr. & vb. n. Concentrating.] [Pref. con-
   + L. centrum center. Cf. Concenter.]
   1. To bring to, or direct toward, a common center; to unite
      more closely; to gather into one body, mass, or force; to
      fix; as, to concentrate rays of light into a focus; to
      concentrate the attention.
      [1913 Webster]

            (He) concentrated whole force at his own camp.
                                                  --Motley.
      [1913 Webster]

   2. To increase the strength and diminish the bulk of, as of a
      liquid or an ore; to intensify, by getting rid of useless
      material; to condense; as, to concentrate acid by
      evaporation; to concentrate by washing; -- opposed to
      dilute.
      [1913 Webster]

            Spirit of vinegar concentrated and reduced to its
            greatest strength.                    --Arbuthnot.

   Syn: To combine; to condense; to consolidate.
        [1913 Webster]

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]

WordNet (r) 3.0 (2006):

concentrated
    adj 1: gathered together or made less diffuse; "their
           concentrated efforts"; "his concentrated attention";
           "concentrated study"; "a narrow thread of concentrated
           ore" [ant: distributed]
    2: of or relating to a solution whose dilution has been reduced
    3: intensely focused; "her concentrated passion held them at
       bay"
    4: (of light) transmitted directly from a pointed light source
       [syn: hard, concentrated] [ant: diffuse, diffused,
       soft]
    5: being the most concentrated solution possible at a given
       temperature; unable to dissolve still more of a substance; "a
       saturated solution" [syn: saturated, concentrated] [ant:
       unsaturated]

Moby Thesaurus II by Grady Ward, 1.0:

118 Moby Thesaurus words for "concentrated":
   advertent, agog, alert, all ears, all eyes, assiduous, attentive,
   aware, axial, careful, centermost, central, centralized, centric,
   centroidal, centrosymmetric, clamped, close, close-knit,
   close-textured, close-woven, compact, compacted, complete,
   compressed, concrete, condensed, congested, conscious,
   consolidated, constricted, contracted, crammed, crammed full,
   cramped, crowded, dense, desperate, diligent, earnest, entire,
   exclusive, exquisite, fierce, finical, finicking, finicky, firm,
   fixed, full-bodied, furious, geocentric, gluey, hard, heavy,
   heedful, impenetrable, impermeable, intense, intent, intentive,
   jam-packed, jammed, key, knitted, lusty, massive, meticulous,
   middle, middlemost, midmost, mindful, nice, niggling, nipped,
   nonporous, observant, observing, omphalic, on the ball, on the job,
   open-eared, open-eyed, openmouthed, packed, pinched, pinched-in,
   pivotal, potent, puckered, pursed, regardful, robust, serried,
   solid, solidified, squeezed, strangled, strangulated, substantial,
   terrible, thick, thick-growing, thickset, total, umbilical,
   undistracted, undivided, unswerving, vehement, vicious, violent,
   viscid, viscose, viscous, wasp-waisted, watchful, wrinkled