penitent

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Feeling or expressing remorse for one's misdeeds or sins; contrite.
• noun One who is penitent.
• noun A person performing penance under the direction of a confessor.

from The Century Dictionary.

• Sorry for sin or for offense committed; contrite; troubled by a sense of guilt and resolved on amendment; repentant.
• Doing penance; suffering.
• noun One who repents, or is sorry for sin, transgression, or offending; a contrite or repentant person.
• noun Eccles., one who makes confession of sin and undergoes, under priestly direction, the ecclesiastical discipline prescribed for its absolution.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who repents of sin; one sorrowful on account of his transgressions.
• noun One under church censure, but admitted to penance; one undergoing penance.
• noun One under the direction of a confessor.
• adjective Feeling pain or sorrow on account of sins or offenses; repentant; contrite; sincerely affected by a sense of guilt, and resolved on amendment of life.
• adjective obsolete Doing penance.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Feeling pain or sorrow on account of sins or offenses; repentant; contrite; sincerely affected by a sense of guilt, and resolved on amendment of life.
• adjective Doing penance.
• noun One who repents of sin; one sorrowful on account of his or her transgressions.
• noun One under church censure, but admitted to penance; one undergoing penance.
• noun One under the direction of a confessor.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective feeling or expressing remorse for misdeeds
• noun (Roman Catholic Church) a person who repents for wrongdoing (a Roman Catholic may be admitted to penance under the direction of a confessor)