penance
Concise Oxford English Dictionary © 2008 Oxford University Press:
penance/ˈpenəns/
▶noun
- 1 punishment inflicted on oneself as an outward expression of repentance for wrongdoing.
- 2 a sacrament in which a member of the Church confesses sins to a priest and is given absolution.
■ a religious observance or other duty imposed as part of this sacrament.
– origin ME: from OFr., from L. paenitentia ‘repentance’, from paenitere ‘be sorry’.
'penance' also found in these Oxford entries:

