The Collaborative International Dictionary of English v.0.48:

Hangdog \Hang"dog`\ (-d[o^]g`), n.
   A base, degraded person; a sneak; a gallows bird.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hangdog \Hang"dog`\, a.
   Low; sneaking; ashamed.
   [1913 Webster]

         The poor colonel went out of the room with a hangdog
         look.                                    --Thackeray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hangdog
    adj 1: showing a sense of guilt; "a guilty look"; "the hangdog
           and shamefaced air of the retreating enemy"- Eric
           Linklater [syn: guilty, hangdog, shamefaced,
           shamed]
    2: frightened into submission or compliance

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "hangdog":
   abashed, abject, ashamed, backscratching, beggarly, blushing,
   bootlicking, chagrined, chapfallen, cowering, crawling,
   crestfallen, cringing, crouching, crushed, embarrassed, fawning,
   flattering, footlicking, groveling, humbled, humiliated,
   ingratiating, mealymouthed, mortified, obeisant, obsequious,
   on bended knee, out of countenance, parasitic, prostrate,
   red-faced, shamed, shamefaced, shamefast, sniveling, sponging,
   sycophantic, timeserving, toadeating, toadying, toadyish,
   truckling