Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

         The princes of the country clustering together. --Foxe.

Source : WordNet®

clustering
     n : a grouping of a number of similar things; "a bunch of
         trees"; "a cluster of admirers" [syn: {bunch}, {clump}, {cluster}]

Source : Free On-Line Dictionary of Computing

clustering
     
        {cluster}