The Collaborative International Dictionary of English v.0.48:

Adumbration \Ad`um*bra"tion\, n. [L. adumbratio.]
   1. The act of adumbrating, or shadowing forth.
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   2. A faint sketch; an outline; an imperfect portrayal or
      representation of a thing.
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            Elegant adumbrations of sacred truth. --Bp. Horsley.
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   3. (Her.) The shadow or outlines of a figure.
      [1913 Webster]

WordNet (r) 3.0 (2006):

adumbration
    n 1: the act of providing vague advance indications;
         representing beforehand [syn: prefiguration,
         foreshadowing, adumbration]
    2: a sketchy or imperfect or faint representation