The word "无忧无虑" is formed by the repetition of the negating character "无" (without) paired with two synonymous characters for mental distress: "忧" (worry) and "虑" (anxiety). This creates a parallel four-character structure where "无忧" and "无虑" are combined, producing a literal meaning of "without worry and without anxiety" to express a state of being completely carefree.