Which word indicates feeling remorse for one’s sins?

The word "penitent" specifically refers to the feeling of remorse or sorrow for having committed sins or wrongdoings. It derives from a process of acknowledgment of one’s actions and the desire to seek forgiveness or make amends. This term is commonly used in religious and moral contexts, emphasizing an emotional and spiritual aspect of regret tied to one's behavior.

In contrast, the other options do not convey this meaning. "Pliant" refers to being easily influenced or flexible, "ponderous" relates to something heavy or difficult to handle, and "plebeian" indicates something common or lower class in social status. None of these terms capture the concept of feeling remorse for one's sins, making "penitent" the clear choice for the definition sought in the question.