from The American Heritage® Dictionary of the English Language, 5th Edition.

  • intransitive verb To make thin or less dense, as air.
  • intransitive verb To purify or refine.
  • intransitive verb To become thin or less dense.

from The Century Dictionary.

  • To make rare, thin, porous, or less dense; expand or enlarge without adding any new matter; figuratively, to spread or stretch out; distend: opposed to condense.
  • To become rare; pass into a thinner or less dense condition.

from the GNU version of the Collaborative International Dictionary of English.

  • intransitive verb To become less dense; to become thin and porous.
  • transitive verb To make rare, thin, porous, or less dense; to expand or enlarge without adding any new portion of matter to; -- opposed to condense.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • verb To make rare, thin, porous, or less dense
  • verb To expand or enlarge without adding any new portion of matter to.

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

  • verb lessen the density or solidity of
  • verb weaken the consistency of (a chemical substance)
  • verb make more subtle or refined


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

[Middle English rarefien, from Old French rarefier, from Medieval Latin rārificāre, alteration of Latin rārēfacere : rārus, rare + facere, to make; see dhē- in Indo-European roots.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

rare +‎ -fy


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  • I'm no stranger to the Gentri-verse and I ride my bike all the time, and I can't even relate to him--which, I guess, is why I also can't always relate to the "bike culture," since they seem so determined to rarefy the normal.

    BSNYC Fridaculous Fun Quiz!

  • Because the elements, on the other hand, can be rarefied and condensed, they can incline the lumen in themselves away from the center of the universe, so as to rarefy it, or toward the center so as to condense it, and this accounts for their natural capacity to move up and down.

    Robert Grosseteste

  • Special clamps can be made to hold the cottle in position and are very convenient if many moulds are to be made, but this is rarefy done.

    6. Mouldmaking and Plaster of Paris

  • NOTE. — _fy_, meaning to make, is found as a suffix in derivatives too numerous to mention; as, purify (to _make pure_), rarefy (to _make rare_), classify (to _make_ or put into a _class_), etc.

    Orthography As Outlined in the State Course of Study for Illinois

  • The arid plains from which the conglomerate crops out rarefy the superincumbent air-stratum to such a degree that the intensely chilled layers resting on the closely adjoining snow-peaks pour down to reëstablish equilibrium, with the wrathful force of an invisible cataract, eight, ten, even seventeen thousand feet in height.

    The Atlantic Monthly, Volume 13, No. 78, April, 1864

  • MISCELLANEOUS WORDS: annual laundry schedule awkward leisure separate beneficial lenient Spaniard decimal license speak exhilarate mechanical specimen familiarize mediæval speech fiber medicine spherical fibrous militia subtle genuine motor surely gluey negotiate technical height origin tenement hideous pacified their hundredths phalanx therefore hysterical physique thinnest icicle privilege until irremediable prodigies vengeance laboratory rarefy visible laid rinse wherein larynx saucer yielding

    Practical Grammar and Composition

  • I shall protest the roving apeman tribes, the sheep-people munching the far fields prayed on by the feudal land-baron wolves who rarefy themselves in the few skyscraper summits and horde unremembered foods.

    The Machineries of Joy

  • But as such means are not at disposal, it becomes necessary to place the terminal in a bulb and rarefy the air in the same.

    Experiments with Alternate Currents of High Potential and High Frequency

  • It is certainly possible to take a hollow core of copper, rarefy the gas in the same, and by passing impulses of sufficiently high frequency through a circuit around it, bring the gas inside to a high degree of incandescence; but as to the nature of the forces there would be considerable uncertainty, for it would be doubtful whether with such impulses the copper core would act as a static screen.

    Experiments with Alternate Currents of High Potential and High Frequency

  • Our condensers, which compress, cool, and rarefy air, enabling travellers to obtain water and even ice from the atmosphere, are great aids in desert exploration, removing absolutely the principal distress of the ancient caravan.

    A Journey in Other Worlds


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