There are a variety of synonyms that can be used to describe becoming inflexible. One such term is "rigid," which implies a lack of adaptability or flexibility. Another term is "unyielding," which suggests that a person or situation is not willing to bend or compromise. "Stiff" is another word that can be used to describe someone who has become inflexible, as it suggests a person who is resistant to change. Similarly, "intractable" conveys a sense of being difficult to manage or control. Finally, "obstinate" implies a stubborn refusal to change one's position or beliefs, which can contribute to becoming inflexible.