Which term refers to the concept of duty in Roman ethical thought, as expressed in Cicero's writings?

The term that refers to the concept of duty in Roman ethical thought, particularly as articulated in Cicero's writings, is "officium." In Roman philosophy and ethics, officium signifies one's duty or obligation to act in a certain manner, often in the context of relationships with others and the responsibilities that come with one's role in society.

Cicero discusses officium as a guiding principle for moral behavior, emphasizing that individuals have duties that govern their actions toward family, community, and the state. This concept is pivotal in understanding Roman moral philosophy, as it reflects the social and ethical expectations of individuals.

The other terms, while relevant in the context of Roman thought, focus on different aspects. "Virtus" relates more to virtue or moral excellence, "ius" pertains to law or rights, and "mos" refers to customs or social norms. Each of these concepts plays a role in Roman moral thought, but none encapsulates the idea of duty in the same way that officium does according to Cicero.