Penitence, repentance, contrition, attrition, compunction, remorse denote sorrow or regret for sin or wrongdoing.
Penitence implies little more than such sorrow or regret.
Repentance is richer in its implications, for it also implies a change of heart, an awareness of one's shortcomings morally or spiritually, or of the evil of one's actions or life as a whole.
Contrition and attrition are both theological terms, and as such contrasted; only contrition is found in general use. Both imply deep sorrow for sin and the purpose of amendment, but in theological use contrition implies that one's sorrow arises out of love of God and a realization of one's failure to respond to his graces, and attrition that it arises from a lower motive, such as fear of hell or fear of the loss of heaven.
In general use contrition implies penitence that is manifest in signs of pain or grief.
Compunction and remorse both imply a painful sting of conscience, but compunction usually suggests a momentary reaction not only for something already done, but also for something being done or to be done, and remorse usually suggests prolonged and insistent self-reproach and often intense suffering for past wrongs and especially for those whose consequences cannot be escaped.