Stubbornly refusing to listen to others or change your mind, even when it might be a good idea.
From 'bull' + 'headed', comparing a person's inflexibility to the thick skull and determined nature of a bull. The compound emerged in American English in the 19th century to describe someone as obstinate as a bull.
Bulls have incredibly thick skulls with dense bone—a bull's head can weigh up to 40 pounds and is nearly solid—so calling someone 'bullheaded' is actually comparing them to an animal literally designed to charge ahead without stopping!
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