Which word describes something that is beneficial or favorable?

The word "boon" describes something that is beneficial or favorable. It refers to a timely benefit or blessing that contributes positively to a situation or person's life. For example, a new technology that improves productivity can be considered a boon for a business. This captures the essence of how the term conveys positivity and advantage, distinguishing it from the other options that do not share this meaning.

In contrast, the other words represent different concepts: an adversary refers to an opponent or enemy, cessation refers to a stopping or termination, and lackluster describes something that is dull or lacking in energy or brilliance. These other terms do not convey the sense of favorability or benefit that "boon" does.