1.  penance(n = noun.feeling) penitence, repentance - remorse for your past conduct;
is a kind of compunction, remorse, self-reproach

2.  penance(n = noun.act) - a Catholic sacrament; repentance and confession and atonement and absolution;
is a kind of sacrament
has parts: absolution, remission, remission of sin, remittal
has particulars: confession

3.  penance(n = noun.act) self-abasement, self-mortification - voluntary self-punishment in order to atone for some wrongdoing;
is a kind of penalisation, penalization, penalty, punishment

1.  Repentance. Wyclif (Luke xv. 7). [1913 Webster]

2.  Pain; sorrow; suffering. Chaucer. [1913 Webster]

3.  A means of repairing a sin committed, and obtaining pardon for it, consisting partly in the performance of expiatory rites, partly in voluntary submission to a punishment corresponding to the transgression, imposed by a confessor or other ecclesiastical authority. Penance is the fourth of seven sacraments in the Roman Catholic Church. Schaff-Herzog Encyc. [1913 Webster]
"And bitter penance, with an iron whip." [1913 Webster]
"Quoth he, “The man hath penance done,
And penance more will do.”" [1913 Webster]

4.  Any act performed by a person to atone for an offense to another; an act of atonement. [PJC]

   To impose penance; to punish. Keats. [1913 Webster]

penance, n. & v.
--n.
1 an act of self-punishment as reparation for guilt.
2 a (in the RC and Orthodox Church) a sacrament including confession of and absolution for a sin. b a penalty imposed esp. by a priest, or undertaken voluntarily, for a sin.
--v.tr. impose a penance on.

Idiom:
do penance perform a penance.

Etymology:
ME f. OF f. L paenitentia (as PENITENT)

N  penalty, retribution, pain, pains and penalties, weregild, wergild, peine forte et dure, penance, the devil to pay, fine, mulct, amercement, forfeit, forfeiture, escheat, damages, deodand, sequestration, confiscation, premunire, doomage.

N  rite, ceremony, ritual, liturgy, ceremonial, ordinance, observance, function, duty, form, formulary, solemnity, sacrament, incantation, service, psalmody, ministration, preaching, preachment, predication, sermon, homily, lecture, discourse, pastoral, baptism, christening, chrism, circumcision, baptismal regeneration, font, confirmation, imposition of hands, laying on of hands, ordination, excommunication, Bar Mitzvah, Bas Mitzvah, Bris, Eucharist, Lord's supper, communion, the sacrament, the holy sacrament, celebration, high celebration, missa cantata, asperges, offertory, introit, consecration, consubstantiation, transubstantiation, real presence, elements, mass, high mass, low mass, dry mass, matrimony, burial, visitation of the sick, seven sacraments, impanation, subpanation, extreme unction, viaticum, invocation of saints, canonization, transfiguration, auricular confession, maceration, flagellation, sackcloth and ashes, penance, telling of beads, processional, thurification, incense, holy water, aspersion, relics, rosary, beads, reliquary, host, cross, rood, crucifix, pax, pyx, agnus Dei, censer, thurible, patera, eileton, Holy Grail, prayer machine, prayer wheel, Sangraal, urceus, ritualism, ceremonialism, sabbatism, sabbatarianism, ritualist, sabbatarian, holyday, feast, fast, Sabbath, Pentecost, Advent, Christmas, Epiphany, Lent, Passion week, Holy week, Easter, Easter Sunday, Whitsuntide, agape, Ascension Day, Candlemas, Ash Wednesday, Good Friday, Holy Thursday, Lammas, Martinmas, Michaelmas, All SAint's DAy, All Souls' Day, Ramadan, Ramazan, Bairam Passover, Shabuoth, Yom Kippur, Day of Atonement, Rosh Hashana, New Year, Hanukkah, Chanukkah, Feast of Lights, Purim, Feast of lots, ritual, ritualistic, ceremonial, baptismal, eucharistical, paschal, what art thou, thou idol ceremony?.

N  penitence, contrition, compunction, repentance, remorse, regret, self-reproach, self-reproof, self-accusation, self-condemnation, self-humiliation, stings of conscience, pangs of conscience, qualms of conscience, prickings of conscience, twinge of conscience, twitch of conscience, touch of conscience, voice of conscience, compunctious visitings of nature, acknowledgment, confession, apology, recantation, penance, resipiscence, awakened conscience, deathbed repentance, locus paenitentiae, stool of repentance, cuttystool, penitent, repentant, Magdalen, prodigal son, a sadder and a wiser man, penitent, repenting, repentant, contrite, conscience- smitten, conscience-stricken, self-accusing, self-convicted, penitential, penitentiary, reclaimed, reborn, not hardened, unhardened, mea culpa, peccavi, erubuit, salva res est, Tu l'as voulu, Georges Dandin, and wet his grave with my repentant tears.

N  atonement, reparation, compromise, composition, compensation, quittance, quits, expiation, redemption, reclamation, conciliation, propitiation, indemnification, redress, amends, apology, amende honorable, satisfaction, peace offering, sin offering, burnt offering, scapegoat, sacrifice, penance, fasting, maceration, sackcloth and ashes, white sheet, shrift, flagellation, lustration, purgation, purgatory.

N  asceticism, puritanism, sabbatarianism, cynicism, austerity, total abstinence, nephalism, mortification, maceration, sackcloth and ashes, flagellation, penance, fasting, martyrdom, ascetic, anchoret, anchorite, martyr, Heautontimorumenos, hermit, puritan, sabbatarian, cynic, sanyasi, yogi, ascetic, austere, puritanical, cynical, over-religious, acerbic.