Which term describes a morally unprincipled person?

The term that describes a morally unprincipled person is "reprobate." This word is often used to refer to individuals who engage in behavior that is considered immoral or sinful. A reprobate may exhibit a lack of principles and an inclination towards wickedness, which aligns with the concept of someone who acts without regard for moral standards.

In contrast, the term "recalcitrant" typically describes someone who is resistant to authority or control; it does not inherently carry a moral connotation. "Sanguinary" relates to bloodshed or violence, often describing something that is bloodthirsty rather than morally lacking. "Sedulous," on the other hand, refers to someone showing dedication and diligence in their work, which is more about industriousness than moral principles. Thus, "reprobate" is the most accurate term for a morally unprincipled person.