from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.
  • n. The region in which this occurs.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. a reduction in the density of a material, especially that of a fluid

from the GNU version of the Collaborative International Dictionary of English

  • n. The act or process of rarefying; the state of being rarefied; -- opposed to condensation.

from The Century Dictionary and Cyclopedia

  • n. The act or process of rarefying or making rare, or of expanding or distending a body or mass of matter, whereby the bulk is increased, or a smaller number of its particles occupy the same space; also, the state or condition so produced: opposed to condensation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a decrease in the density of something


Sorry, no etymologies found.


  • But if, for example, the rise in the emulsion to double the rarefaction is a milliard times less than in oxygen, it means that the effective weight of the grain is a milliard times greater than that of the oxygen molecule.

    Jean Baptiste Perrin - Nobel Lecture

  • He is also studying the process of rarefaction, which is when capillaries and vessels start losing their density.

    The Charleston Gazette -

  • Instead, they used a theoretical approach called rarefaction for gene discovery, a process developed for ecological surveys to determine the abundance of a species in an ecosystem.

    EurekAlert! - Breaking News

  • Such quantity, however, should not be identified with the determinate dimensions a body possesses, but is rather a quantitas which remains the same during processes such as rarefaction and condensation.

    Giles of Rome

  • When it comes to estimating how many species are yet to be discovered, Webb says scientists use a technique called "rarefaction": "Imagine a garden pond.

    How did they count all the fish in the sea?

  • The Dictionary of Islam by Thomas Patrick Hughes states: “They become invisible at please (by a rapid extension or rarefaction of the particles which compose them), or suddenly disappear in the earth or air, or through a solid wall.”

    SciFi, Fantasy & Horror Collectibles - Part 1065

  • Boyle suggested that the divergence from the expected result in the case of rarefaction may have been due to "some little aerial bubbles in the quicksilver" ( "so easy is it in such nice experiments to miss of exactness," he added).

    Sticky Wants to Grab

  • The results are set out, with misprints, in two tables, and Boyle's conclusion was that the experimental findings matched the predicted results very well in the case of compression, less well in the case of rarefaction.

    Sticky Wants to Grab

  • This move becomes evident in certain physical questions, e.g., in the study of condensation and rarefaction, where Albert openly disagrees with his Parisian master by arguing that condensation and rarefaction are possible only through the local motion of the parts of a body, and without needing to assume some quantity that would have a distinct reality on its own.

    Albert of Saxony

  • He calls her feminine because he has no better word: the feminine, a higher rarefaction of the female, to the point of becoming spirit.

    From 'Summertime': 'Undated Fragments'


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  • I unda-stand! Its a rare density and/or a dense rarity! Meracious (untruth) fingere!

    October 9, 2011

  • “I do not know,” he began, “if you have ever considered the nature of sound. Suffice to say that it consists of a series of waves moving through the air. Not, however, waves like those on the surface of the sea — oh dear no! Those waves are up and down movements. Sound waves consist of alternate compressions and rarefactions.”



    “Don’t you mean rarefications’?”

    “I do not. I doubt if such a word exists, and if it does, it shouldn’t,” retorted Purvis, with the aplomb of Sir Alan Herbert dropping a particularly revolting neologism into his killing-bottle. . . .

                                    — Arthur C. Clarke. “Silence, Please”.

    October 9, 2011