Which word best defines someone characterized by an insatiable appetite or eagerness for something?

The word "voracious" is the best choice to describe someone characterized by an insatiable appetite or eagerness for something. It originates from the Latin word "vorare," which means "to devour." This term is typically used to convey a strong, almost unquenchable desire, whether for food, knowledge, or any other pursuit. When someone is described as voracious, it implies that they have an intense enthusiasm or craving that drives them to seek out whatever it is they desire, often with great intensity.

The other options, while having distinct meanings, do not capture the same essence of insatiability or eagerness. "Viable" refers to something capable of working successfully or being feasible, which doesn't relate to eagerness. "Voluminous" describes something that is large in volume or size, often used in context with physical objects or texts, rather than appetite or eagerness. "Vivacious" pertains to someone who is lively and animated, emphasizing energy and spirit rather than the specific notion of an insatiable desire. Thus, "voracious" stands out as the term that most accurately conveys the idea of a deep and relentless quest for something.