The antonyms of "underexplored" are plentiful, as this word implies that something has not been adequately studied, investigated, or understood. Some possible antonyms for "underexplored" might include fully explored, comprehensively researched, clearly understood, thoroughly investigated, exhaustively examined, deeply analyzed, and extensively studied. Other antonyms might include well-developed, extensively practiced, widely understood, thoroughly tested, widely accepted, and widely recognized. In each case, the antonym suggests a level of knowledge or understanding that is greater than what is implied by the word "underexplored," indicating a greater degree of expertise or familiarity in a particular area.