penance vs self-mortification

penance and self-mortification both are nouns.

Word	Noun	Adjective	Verb	Adverb
penance	Yes	No	No	No
self-mortification	Yes	No	No	No

As nouns, penance and self-mortification are synonyms defined as:

penance and self-mortification: voluntary self-punishment in order to atone for some wrongdoing

Other synonyms of penance include self-abasement.

penance (noun)	self-mortification (noun)
voluntary self-punishment in order to atone for some wrongdoing	voluntary self-punishment in order to atone for some wrongdoing
a Catholic sacrament; repentance and confession and atonement and absolution
remorse for your past conduct