The word "莽汉" is formed by combining the character "莽", which conveys meanings of recklessness, rashness, or crude roughness, with the character "汉", which refers to a man or fellow. Together, they create a compound term where "莽" describes the attribute of the man denoted by "汉", resulting in a word that specifically means a reckless, impulsive, or rough-mannered man.