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

Moby Thesaurus II by Grady Ward, 1.0:

146 Moby Thesaurus words for "formative":
   IC analysis, abecedarian, aboriginal, accidence, adaptable, affix,
   affixation, allomorph, antenatal, autochthonous, beginning,
   behind the scenes, bendable, bending, bound morpheme, budding,
   causal, causative, compliant, component, conjugation, constituent,
   constitutive, constructive, creative, cutting, decisive,
   declension, demiurgic, derivation, determinative,
   difference of form, ductile, effectual, elastic, elemental,
   elementary, embryonic, enclitic, etiological, extensible,
   extensile, fabricable, facile, fetal, fictile, flexible, flexile,
   flexuous, formable, formal, formational, foundational, free form,
   fundamental, generative, gestatory, giving,
   immediate constituent analysis, impressible, impressionable,
   in embryo, in its infancy, in the bud, inaugural, inceptive,
   inchoate, inchoative, incipient, incunabular, infant, infantile,
   infix, infixation, inflection, initial, initiative, initiatory,
   institutive, integral, integrant, introductory, inventive,
   like putty, limber, lissome, lithe, lithesome, malleable, moldable,
   morph, morpheme, morphemic analysis, morphemics, morphology,
   morphophonemics, morphotic, nascent, natal, occasional, original,
   originative, paradigm, parturient, pivotal, plastic, pliable,
   pliant, postnatal, prefix, prefixation, pregnant, prenatal, primal,
   primary, prime, primeval, primitive, primogenial, proclitic,
   procreative, productive, radical, receptive, responsive, root,
   rudimental, rudimentary, sensitive, sequacious, shapable, springy,
   stem, submissive, suffix, suffixation, supple, susceptible, theme,
   tractable, tractile, ur, whippy, willowy, word-formation,
   yielding