Which word best describes a character trait of being morally principled?

The word "scrupulous" is the best choice to describe a character trait of being morally principled. This term indicates a person who is very attentive to details of ethics and morality, demonstrating a strong sense of right and wrong. A scrupulous individual ensures that their actions align with their moral values, acting with integrity and conscientiousness in their decisions and behaviors.

In contrast, "invulnerable" refers to being immune to harm or incapable of being wounded, which does not capture the essence of moral principles. "Supercilious" describes an attitude of being disdainful or condescending toward others, which is typically associated with arrogance rather than moral integrity. Lastly, "nonchalant" denotes a casual or relaxed demeanor, often suggesting a lack of concern or indifference, which is not aligned with the conscientiousness implied by being scrupulous. Thus, "scrupulous" is the term that most accurately embodies the idea of being grounded in moral principles.