[rij-id] 
| 1. | stiff or unyielding; not pliant or flexible; hard: a rigid strip of metal. |
| 2. | firmly fixed or set. |
| 3. | inflexible, strict, or severe: a rigid disciplinarian; rigid rules of social behavior. |
| 4. | exacting; thorough; rigorous: a rigid examination. |
| 5. | so as to meet precise standards; stringent: lenses ground to rigid specifications. |
| 6. | Mechanics. of, pertaining to, or noting a body in which the distance between any pair of points remains fixed under all forces; having infinite values for its shear modulus, bulk modulus, and Young's modulus. |
| 7. | Aeronautics.
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