contrite, remorseful, rueful, ruthful
Meaning: feeling or expressing pain or sorrow for sins or offenses
"I begin to think there's truth in the old saw, 'It's hard to teach old dogs new tricks,'" remarked Mr. Travilla, with a comically rueful face. "I've a mind to give it up.
To this, he in the green gaban replied "I, Sir Knight of the Rueful Countenance, am a gentleman by birth, native of the village where, please God, we are going to dine today; I am more than fairly well off, and my name is Don Diego de Miranda.
In short, to sum up all in a few words, or in a single one, I may tell you I am Don Quixote of La Mancha, otherwise called 'The Knight of the Rueful Countenance;' for though self-praise is degrading, I must perforce sound my own sometimes, that is to say, when there is no one at hand to do it for me.