General:
* Rigid: This is a common word for something that is inflexible, unyielding, and resistant to change.
* Inflexible: This word directly means "not flexible" and can be used for both physical and mental inflexibility.
* Stiff: This word often refers to physical rigidity, but can also be used metaphorically for someone who is unwilling to compromise.
* Unbending: This word implies an unwillingness to change or compromise.
* Unyielding: Similar to "unbending", this word signifies a stubborn resistance to change.
Specific to physical flexibility:
* Immovable: This word describes something that cannot be moved or bent.
* Unpliable: This word refers to something that is not easily bent or molded.
Specific to mental flexibility:
* Dogmatic: This word describes someone who holds rigidly to their beliefs and is unwilling to consider other viewpoints.
* Closed-minded: This word describes someone who is unwilling to listen to or consider new ideas.
* Obstinate: This word describes someone who is stubborn and refuses to change their mind.
The best word to use will depend on the specific context and the nuance you want to convey.