Which word refers to adherence to the truth; truthfulness?

The word that refers to adherence to the truth or truthfulness is "veracity." This term encapsulates the quality of being truthful, honest, and reliable in one's statements and representations. It is often used to describe a person's character or the accuracy of information. Veracity is the foundation of trust in communication, whether in personal relationships, journalism, or legal contexts.

In contrast, the other choices present concepts that are opposite or unrelated to truthfulness. "Deceit" entails the act of misleading or deceiving others, which stands in direct opposition to truthfulness. "Falsehood" refers to something that is untrue or a lie, further emphasizing the absence of truth. "Insincerity" denotes a lack of honesty in expressing feelings or intentions, suggesting a failure to be genuine. These terms highlight behaviors or states that involve dishonesty, making "veracity" the clear choice when referring to adherence to the truth.