Which word describes having a reverence for a god?

The term that best describes having a reverence for a god is "piety." Piety specifically refers to the quality of being religious or reverent. It encompasses a deep respect and devotion toward the divine and is often associated with the practices and beliefs of faith.

"Pious," while related to piety, is an adjective that describes a person who is devoutly religious or exhibits piety in their actions. Although it conveys a similar notion of reverence, it does not directly define the quality itself, which is what the question is asking for.

The other options are relevant in related contexts but do not fit the definition as precisely. "Atheistic" refers to the absence of belief in gods, which is contrary to the idea of reverence. "Devotion" implies a strong attachment or commitment to a cause or person, often in a religious context, but it does not specify the reverence for a god itself in the way "piety" does. Thus, "piety" is the most accurate term in this context.