The Chinese idiom **光明正大** (guāngmíng zhèngdà) is formed through the combination and reinforcement of two parallel, synonymous binomial compounds. The first pair, **光明** (guāngmíng), literally "light and bright," metaphorically conveys openness, honesty, and transparency. The second pair, **正大** (zhèngdà), means "upright and great," conveying moral correctness and magnanimity. Together, they form a four-character idiomatic expression (chengyu) where the two halves semantically reinforce each other in a parallel structure, creating a powerful holistic meaning: to act openly, honorably, and with unwavering integrity, without secrecy or deviousness. This formation follows a common chengyu pattern where AABB (where A=光, B=明, A'=正, B'=大) serves to emphasize and elevate the core virtuous concept.