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.

adjective

bending , flexible , lenient , limber , pliable , pliant , soft , yielding

adjective

adamant , adamantine , austere , bullheaded , changeless , chiseled , dead set , definite , determined , exact , firm , fixed , hard , hard-line * , harsh , incompliant , inelastic , inexorable , inflexible , intransigent , invariable , locked in , obdurate , rigorous , set , set in stone , single-minded , solid , static , stern , strait-laced * , stringent , tough nut to crack , unalterable , unbending , unbreakable , unchanging , uncompromising , undeviating , unmoving , unpermissive , unrelenting , unyielding , stiff , immutable , inalterable , ironclad , unchangeable , brassbound , die-hard , grim , implacable , iron , relentless , remorseless , unbendable , uncompliant , demanding , exacting , strict , tough , formal , immovable , inclement , ironhanded , scrupulous , severe , sharp , strait , stubborn , taut , tense , unpliant , unshakable