The Collaborative International Dictionary of English v.0.48:

Gradation \Gra*da"tion\, n., [L. gradatio: cf. F. gradation. See
   Grade.]
   1. The act of progressing by regular steps or orderly
      arrangement; the state of being graded or arranged in
      ranks; as, the gradation of castes.
      [1913 Webster]

   2. The act or process of bringing to a certain grade.
      [1913 Webster]

   3. Any degree or relative position in an order or series.
      [1913 Webster]

            The several gradations of the intelligent universe.
                                                  --I. Taylor.
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   4. (Fine Arts) A gradual passing from one tint to another or
      from a darker to a lighter shade, as in painting or
      drawing.
      [1913 Webster]

   6. (Mus.) A diatonic ascending or descending succession of
      chords.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Gradation \Gra*da"tion\, v. t.
   To form with gradations. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

gradation
    n 1: relative position in a graded series; "always a step
         behind"; "subtle gradations in color"; "keep in step with
         the fashions" [syn: gradation, step]
    2: a degree of ablaut [syn: grade, gradation]
    3: the act of arranging in grades [syn: gradation,
       graduation]