Stubborn Sort is a term used to describe someone who is difficult to persuade or change their opinion. The crossword solutions for this term are ASS, MULE, and CUSS. ASS is a three letter word meaning a donkey or an idiot. MULE is a four letter word meaning a hybrid animal or a stubborn person. CUSS is a four letter word meaning to swear or use profanity. All of these words can be used to describe someone who is stubborn and unwilling to change their opinion.