The word 罪魁祸首 is formed by combining the characters 罪 (crime) and 魁 (chief) to create 罪魁, meaning "chief criminal", and 祸 (disaster) and 首 (head) to create 祸首, meaning "head of disaster". These two parallel compounds are joined to reinforce the concept, resulting in a term that denotes the primary offender or ringleader responsible for a wrongdoing or calamity.