What derivative of fundō means "incapable of producing any useful result"?

The term that derives from fundō and means "incapable of producing any useful result" is indeed "futile." This word comes from the Latin root "futilis," which is closely related to fundō, meaning "to pour out" or "to melt." The concept of futility implies a sense of effort that yields no results or is ineffective, much like pouring something out without a purpose or benefit. In contexts where efforts lead to an absence of worthwhile outcomes, the use of "futile" is particularly apt. This connection to the idea of being poured out or wasted aligns perfectly with the definition provided.

"Fruitless," "unproductive," and "benefits," while they share some semantic space with the idea of not achieving useful results, do not have the same direct link to the concept of being devoid of results as "futile" does. Thus, "futile" is the most precise choice in this case.