Definition of rarefaction in US English:


(also rarifaction)


  • 1Diminution in the density of something, especially air or a gas.

    ‘opposed processes such as rarefaction and condensation’
    count noun ‘a series of rarefactions and compactions’
    • ‘Anaximenes' notion of successive change of matter by rarefaction and condensation was influential in later theories.’
    • ‘We hear nothing more of ‘separating out’ or even of rarefaction and condensation.’
    • ‘Sound is a wave of compression and rarefaction in air.’
    • ‘Likewise, in a famous passage, Buridan is driven by his own experience to reject Ockham's explanation of condensation and rarefaction as kinds of locomotion.’
    • ‘However, definitions which focus on the idea of either irreversible collapse or of bellows-like compression and rarefaction of air are no help in the present context.’
    purification, refining, clarifying, clarification, cleansing, straining, sifting, filtering, filtration, distillation, concentration, processing, treatment, treating
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    1. 1.1Medicine The lessening of density of tissue, especially of nervous tissue or bone.
      ‘the cord has undergone rarefaction’
      • ‘Loss of pain sensation together with possible rarefaction of the bones of the neuropathic foot can have serious consequences.’
      • ‘Histologic examination of the brain showed extensive neuronal loss, gliosis, rarefaction, scarring, and foci of chronic inflammation in multiple brain regions.’
      • ‘Due to the relatively advanced age of the patients included in our study, marked rarefaction of the spongy bone tissue was present, but signs of metabolic bone disease, that is, osteomalacia, were not found in any of the cases.’
      • ‘Hypertension is characterized by capillary rarefaction, a reduction of the number of capillaries per volume of tissue.’
      • ‘Numerous platelets appeared in the lumen, some of which showed signs of degeneration with swelling and rarefaction.’


Early 17th century: from medieval Latin rarefactio(n-), from the verb rarefacere ‘grow thin, become rare’.