The word "乖乖" is formed through the process of reduplication, where the single character "乖" (guāi), which carries the core meaning of being well-behaved, obedient, or clever, is simply repeated. This repetition does not change the fundamental meaning but intensifies it, adding a strong layer of endearment, affection, and softness. The resulting term feels more intimate, rhythmic, and often conveys a tone of tenderness, making it a common term of address for children or a soothing expression of admonishment.