The word "绵绵" is formed by reduplicating the character 绵, a phonetic-semantic compound where the silk radical (纟) conveys association with fineness or softness, and the component "帛" provides phonetic cues. This repetition creates an adjective that intensifies the original meaning of 绵, emphasizing a continuous, unbroken, or prolonged state, as in describing incessant rain or enduring emotions.