What is a synonym for "obstinate"?

The term "obstinate" refers to someone who is stubbornly refusing to change their opinion or chosen course of action, despite attempts to persuade them to do so. Therefore, a synonym for "obstinate" is "stubborn." Both words convey a similar meaning of being unyielding and determined in one's position, making "stubborn" the most fitting choice.

In contrast, the other terms—flexible, agreeable, and cooperative—convey a willingness to adapt or compromise, which contrasts with the essence of being obstinate. Flexible refers to the ability to change or be adjusted easily; agreeable suggests a tendency to go along with others' ideas; and cooperative indicates a willingness to work together. Each of these options represents a more accommodating attitude, which is the opposite of what "obstinate" embodies.