Which word can be defined as overly elaborate or complicated?

The term "involute" is often used to describe something that is intricate, complex, or overly elaborate, particularly in geometry or describing forms that are rolled or coiled inward. In a broader context, it can convey a sense of something that is convoluted or needlessly complicated. This aligns well with the definition of being overly elaborate.

While the other choices hold distinct meanings, they do not convey the same sense of complexity or elaborateness as "involute." "Jejune" refers to something that is simplistic or dull, "meretricious" denotes something that is superficially attractive but lacking in real value or quality, and "mettle" pertains to a person's ability to cope with difficulties in a spirited and resilient manner. Thus, the best fit for the given definition is "involute," highlighting its association with intricacy and complication.