The Collaborative International Dictionary of English v.0.48:

Formative \Form"a*tive\, a. [Cf. F. formatif.]
   1. Giving form; having the power of giving form; plastic; as,
      the formative arts.
      [1913 Webster]

            The meanest plant can not be raised without seed, by
            any formative residing in the soil.   --Bentley.
      [1913 Webster]

   2. (Gram.) Serving to form; derivative; not radical; as, a
      termination merely formative.
      [1913 Webster]

   3. (Biol.) Capable of growth and development; germinal; as,
      living or formative matter.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Formative \Form"a*tive\, n. (Gram.)
      (a) That which serves merely to give form, and is no part
          of the radical, as the prefix or the termination of a
          word.
      (b) A word formed in accordance with some rule or usage,
          as from a root.
          [1913 Webster]

WordNet (r) 3.0 (2006):

formative
    adj 1: capable of forming new cells and tissues; "a formative
           zone in developing bone"
    2: forming or capable of forming or molding or fashioning; "a
       formative influence"; "a formative experience" [syn:
       formative, shaping, plastic]
    n 1: minimal language unit that has a syntactic (or
         morphological) function