Rigid (adjective)

1. Not able to bend or be forced out of shape; stiff.
2. Inflexible in opinions, attitudes, or behavior.

Origin:

Late middle english: from latin rigidus, from rigere 'be stiff', from rigor 'stiffness'.

Examples:

1. The metal pipe was rigid and wouldn't bend.
2. The rules were very rigid and inflexible.
3. The ship's hull was made of rigid plastic.
4. The teacher's grading policy was rigid and unfair.
5. Her rigid stance on the issue made it difficult to find a solution.