The Collaborative International Dictionary of English v.0.48:

Adumbrate \Ad*um"brate\, v. t. [L. adumbratus, p. p. of
   adumbrare; ad + umbrare to shade; umbra shadow.]
   [1913 Webster]
   1. To give a faint shadow or slight representation of; to
      outline; to shadow forth.
      [1913 Webster]

            Both in the vastness and the richness of the visible
            universe the invisible God is adumbrated. --L.
                                                  Taylor.
      [1913 Webster]

   2. To overshadow; to shade.
      [1913 Webster]

WordNet (r) 3.0 (2006):

adumbrate
    v 1: describe roughly or briefly or give the main points or
         summary of; "sketch the outline of the book"; "outline his
         ideas" [syn: sketch, outline, adumbrate]
    2: give to understand; "I insinuated that I did not like his
       wife" [syn: intimate, adumbrate, insinuate]