Source : Webster's Revised Unabridged Dictionary (1913)

Rueful \Rue"ful\, a.
   1. Causing one to rue or lament; woeful; mournful; sorrowful.

   2. Expressing sorrow. ``Rueful faces.'' --Dryden.

            Two rueful figures, with long black cloaks. --Sir W.
                                                  Scott.
      -- {Rue"ful*ly}, adv. -- {Rue"ful*ness}, n.

Source : WordNet®

rueful
     adj : feeling or expressing pain or sorrow for sins or offenses
           [syn: {contrite}, {remorseful}, {ruthful}, {sorry}]