stiff or unyielding; not pliant or flexible; hard

a rigid strip of metal.

firmly fixed or set.

inflexible, strict, or severe

a rigid disciplinarian; rigid rules of social behavior.

exacting; thorough; rigorous

a rigid examination.

so as to meet precise standards; stringent

lenses ground to rigid specifications.

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.

Aeronautics .

(of an airship or dirigible) having a form maintained by a stiff, unyielding structure contained within the envelope.

pertaining to a helicopter rotor that is held fixedly at its root.

noun

die-hardism , grimness , implacability , implacableness , incompliance , incompliancy , inexorability , inexorableness , inflexibility , inflexibleness , intransigence , intransigency , obduracy , obdurateness , relentlessness , remorselessness , rigidness , austerity , hardness , harshness , rigor , rigorousness , sternness , strictness , stringency , toughness