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:

Cluster \Clus"ter\, v. i. [imp. & p. p. Clustered; p. pr. &
   vb. n. Clustering.]
   To grow in clusters or assemble in groups; to gather or unite
   in a cluster or clusters.
   [1913 Webster]

         His sunny hair
         Cluster'd about his temples, like a god's. --Tennyson.
   [1913 Webster]

         The princes of the country clustering together. --Foxe.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

clustered \clustered\ adj.
   1. growing close together but not in dense mats; -- of
      plants.
      [WordNet 1.5]

   2. occurring close together in bunches or clusters.

   Syn: bunched, bunchy.
        [WordNet 1.5]

   3. clustered together but not coherent.

   Syn: agglomerate, agglomerated, agglomerative, aggregate.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

clustered
    adj 1: growing close together but not in dense mats
    2: clustered together but not coherent; "an agglomerated flower
       head" [syn: agglomerate, agglomerated, agglomerative,
       clustered]