The word "叮叮" is formed by repeating the single character "叮", which is a pictophonetic compound consisting of the semantic radical "口" (kǒu), denoting mouth or sound, and the phonetic component "丁" (dīng), which cues its pronunciation. This duplication results in an onomatopoeic word that mimics a repeated light, sharp sound, like a ding or a tinkling.