The Collaborative International Dictionary of English v.0.48:

Shamefaced \Shame"faced`\, a. [For shamefast; AS. scamfaest. See
   Shame, n., and Fast firm.]
   Easily confused or put out of countenance; diffident;
   bashful; modest.
   [1913 Webster]

         Your shamefaced virtue shunned the people's prise.
                                                  --Dryden.
   [1913 Webster]

   Note: Shamefaced was once shamefast, shamefacedness was
         shamefastness, like steadfast and steadfastness; but
         the ordinary manifestations of shame being by the face,
         have brought it to its present orthography. --Trench.
         [1913 Webster] -- Shame"faced, adv. --
         Shame"faced`ness, n.
         [1913 Webster]

WordNet (r) 3.0 (2006):

shamefacedness
    n 1: feeling embarrassed about yourself [syn: shamefacedness,
         sheepishness]