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See more synonyms for rarefy on Thesaurus.com
verb (used with object), rar·e·fied, rar·e·fy·ing.
  1. to make rare or rarer; make less dense: to rarefy a gas.
  2. to make more refined, spiritual, or exalted.
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verb (used without object), rar·e·fied, rar·e·fy·ing.
  1. to become rare or less dense; become thinned: Moisture rarefies when heated.
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Origin of rarefy

1350–1400; Middle English rarefien < Middle French rarefier < Latin rārēfacere, equivalent to rārē-, combining form of rārus rare1 (for expected rāri-; orig. of -ē- unclear) + facere to make; see -fy
Related formsrar·e·fi·a·ble, adjectiverar·e·fi·er, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words


Examples from the Web for rarefy

Historical Examples

  • But if warm dry winds blow upon the clouds, they rarefy the vapour to a greater degree, and temporarily disperse the clouds.

    The Reason Why


  • The rarefy of the atmosphere continued to affect the wood-work of the wagons, and the wheels were incessantly falling to pieces.

  • But extend this vapour, rarefy it; from so narrow a room as our natural bodies, to any politic body, to a state.

  • The air consequently was damp and gross, for want of stronger rays to open and rarefy it.

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

British Dictionary definitions for rarefy


verb -fies, -fying or -fied
  1. to make or become rarer or less dense; thin out
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Derived Formsrarefiable, adjectiverarefier, noun

Word Origin

C14: from Old French raréfier, from Latin rārēfacere, from rārus rare 1 + facere to make
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 rarefy


late 14c., from Old French rarefier (14c.) and directly from Medieval Latin rarificare, from Latin rarefacere "make rare," from rarus "rare, thin" (see rare (adj.1)) + facere "to make" (see factitious). Related: Rarefied.

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Online Etymology Dictionary, © 2010 Douglas Harper