What word refers to a rule of personal conduct?

The term "precept" is indeed the most appropriate choice to describe a rule of personal conduct. A precept typically refers to a general rule intended to regulate behavior or thought, often derived from moral or ethical considerations. It embodies an ethical guideline or principle that an individual might choose to follow in their daily life, emphasizing personal responsibility and moral integrity.

In contrast, while "dictum" generally refers to an authoritative statement or decree, it does not primarily focus on personal conduct. A "maxim" is similar to a precept but often suggests a more personal or philosophical aphorism rather than a guideline for conduct. "Regulation," on the other hand, implies formal rules or laws that are externally imposed, typically by an organization or government, rather than personal conduct that arises from self-imposed beliefs or ethical considerations. Thus, "precept" encapsulates the idea of a personal conduct rule most effectively.