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):

shamefaced
    adj 1: extremely modest or shy; "cheerfully bearing reproaches
           but shamefaced at praise"- H.O.Taylor
    2: showing a sense of shame [syn: shamefaced, sheepish]
    3: showing a sense of guilt; "a guilty look"; "the hangdog and
       shamefaced air of the retreating enemy"- Eric Linklater [syn:
       guilty, hangdog, shamefaced, shamed]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "shamefaced":
   abashed, ashamed, bashful, blushing, chagrined, chapfallen,
   chastened, confused, conscience-smitten, conscience-stricken,
   conscious, coy, crestfallen, crushed, demure, diffident,
   discomfited, embarrassed, full of remorse, hangdog, humbled,
   humiliated, inarticulate, meek, modest, mortified, mousy,
   out of countenance, red-faced, regretful, remorseful, repining,
   rueful, self-accusing, self-condemning, self-conscious,
   self-convicting, self-debasing, self-effacing, self-flagellating,
   self-humiliating, self-punishing, self-reproaching, shamed,
   shamefast, shameful, sheepish, shy, skittish, sorry, stammering,
   timid, timorous, uncomfortable, unhappy about, wistful