The term INFLEXIBLE ONE can be summarized by two crossword solutions: CUSS (4 letters) and HARDLINER (9 letters). CUSS is a slang term for an angry outburst, usually involving profanity. It is often used to express frustration or disapproval. HARDLINER is a term used to describe someone who is uncompromising in their views and unwilling to compromise. This term is often used to describe political figures who are unwilling to negotiate or compromise on their beliefs. Together, these two terms describe someone who is inflexible and unwilling to change their views.