The word "缠绵悱恻" is formed by combining two two-character compounds: "缠绵", from 缠 (entangle) and 绵 (soft, continuous), meaning lingering or intertwined, and "悱恻", from 悱 (hesitant to speak) and 恻 (sorrowful), meaning melancholy or poignant. The four-character idiom results from the semantic fusion of these pairs, where each component contributes directly to the overall meaning of deeply entwined sorrow.