The word "唏嘘" is formed by combining two characters, "唏" and "嘘", each containing the mouth radical (口) to denote sound-related meanings, with phonetic components ("希" for "唏" and "虚" for "嘘") indicating pronunciation. Both characters individually refer to sounds like sighing or sobbing, and their combination creates a disyllabic word that intensifies the expression of sighing or lamentation, typically conveying a sense of melancholy or regret.