'penitentiary' originates from Medieval Latin, specifically the word 'penitentiarius,' where 'penitentia' meant 'repentance.'

'penitentiarius' transformed into the Old French word 'penitencier,' and eventually became the modern English word 'penitentiary' through Middle English.

Initially, it meant 'a place for repentance,' but over time it evolved into its current meaning of 'a prison for serious offenders.'