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rigid

[rij-id]
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adjective
  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, relating 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.
    1. (of an airship or dirigible) having a form maintained by a stiff, unyielding structure contained within the envelope.
    2. pertaining to a helicopter rotor that is held fixedly at its root.

Origin of rigid

1530–40; < Latin rigidus, equivalent to rig(ēre) to be stiff, stiffen + -idus -id4
Related formsri·gid·i·ty, rig·id·ness, nounrig·id·ly, adverbo·ver·rig·id, adjectiveo·ver·rig·id·ly, adverbo·ver·rig·id·ness, nouno·ver·ri·gid·i·ty, nounsub·rig·id, adjectivesub·rig·id·ly, adverbsub·rig·id·ness, nounsub·ri·gid·i·ty, nounun·rig·id, adjectiveun·rig·id·ly, adverbun·rig·id·ness, noun

Synonyms

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1. unbending, firm, inflexible. 2. immovable, static. 3. austere, stern, unyielding. See strict. 4, 5. demanding.

Antonyms

1. elastic. 3. lax.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for unrigid

rigid

adjective
  1. not bending; physically inflexible or stiffa rigid piece of plastic
  2. unbending; rigorously strict; severerigid rules
adverb
  1. completely or excessivelythe lecture bored him rigid
Derived Formsrigidly, adverbrigidity or rigidness, noun

Word Origin

C16: from Latin rigidus, from rigēre to be stiff
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for unrigid

rigid

adj.

early 15c., from Latin rigidus "hard, stiff, rough, severe," from rigere "be stiff," from PIE *reig- "stretch (tight), bind tightly, make fast" (cf. Old Irish riag "torture," Middle High German ric "band, string"). Related: Rigidly.

Online Etymology Dictionary, © 2010 Douglas Harper