This term is defined as: Free of deceit and untruthfulness; sincere.

The term that means being free of deceit and untruthfulness while being sincere is best captured by the word "honest." Honesty encompasses not only the absence of lies or deceit but also a commitment to truthfulness and integrity in one's actions and words. Someone who is honest expresses their thoughts and feelings openly, without hiding the truth or misleading others.

While other terms like "transparent," "forthright," and "authentic" also relate to truthfulness and sincerity, they focus on slightly different aspects of communication or identity. For instance, "transparent" often refers to openness in processes or intentions, suggesting clarity and forthrightness in information sharing. "Forthright" implies a direct and straightforward manner in expressing one's views but does not exclusively emphasize sincerity. "Authentic" relates to being genuine and true to oneself, which involves honesty but also encompasses other qualities like individuality and integrity.

Therefore, "honest" is the most comprehensive choice that directly aligns with the definition provided in the question.