IPA: /ˌpɛnɪˈtɛnʃəli/
KK: /pɛnɪˈtɛnʃəli/
In a way that shows regret or sorrow for wrongdoing.
He spoke penitentially, expressing his deep remorse for his actions.
Penitentially → It is formed from "penitential" (from Latin "paenitentialis", meaning relating to repentance) and "-ly" (meaning in a manner of). The word "penitentially" means in a manner relating to repentance or expressing sorrow for wrongdoing.
Think of the word 'penitential' which relates to feeling sorry or regretful, and remember that 'penitentially' means acting in a way that shows this sorrow.