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[vey-per] /ˈveɪ pər/
a visible exhalation, as fog, mist, steam, smoke, or noxious gas, diffused through or suspended in the air:
the vapors rising from the bogs.
Physics. a gas at a temperature below its critical temperature.
a substance converted into vapor for technical or medicinal uses.
a combination of a vaporized substance and air.
gaseous particles of drugs that can be inhaled as a therapeutic agent.
  1. a strange, senseless, or fantastic notion.
  2. something insubstantial or transitory.
vapors, Archaic.
  1. mental depression or hypochondria.
  2. injurious exhalations formerly supposed to be produced within the body, especially in the stomach.
verb (used with object)
to cause to rise or pass off in, or as if in, vapor; vaporize.
Archaic. to affect with vapors; depress.
verb (used without object)
to rise or pass off in the form of vapor.
to emit vapor or exhalations.
to talk or act grandiloquently, pompously, or boastfully; bluster.
Also, especially British, vapour.
Origin of vapor
1325-75; Middle English vapour < Latin vapor steam
Related forms
vaporable, adjective
vaporability, noun
vaporer, noun
vaporless, adjective
vaporlike, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for vapor
Contemporary Examples
Historical Examples
  • This vapor is rendered intensely cold by expansion, and this cold is imparted to the water in tank a to freeze it.

  • The fires are started, and the oil soon begins to turn into vapor.

    Diggers in the Earth Eva March Tappan
  • The nature of its mechanism was hinted at only by a small, frosty wisp of steam or vapor up front.

    Stamped Caution Raymond Zinke Gallun
  • The object of this is to see how hot the oil must be before it gives off a vapor which will burn.

    Diggers in the Earth Eva March Tappan
  • We had hoped to perceive Saint Lucia; but the atmosphere is too heavily charged with vapor to-day.

British Dictionary definitions for vapor


the US spelling of vapour
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
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Word Origin and History for vapor

late 14c., from Anglo-French vapour, from Latin vaporem (nominative vapor) "exhalation, steam, heat," of unknown origin. Vapors "fit of fainting, hysteria, etc." is 1660s, from medieval notion of "exhalations" from the stomach or other organs affecting the brain.

Online Etymology Dictionary, © 2010 Douglas Harper
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vapor in Medicine

vapor va·por (vā'pər)

  1. Barely visible or cloudy diffused matter, such as mist, fumes, or smoke, suspended in the air.

  2. The state of a substance that exists below its critical temperature and that may be liquefied by application of sufficient pressure.

  3. The gaseous state of a substance that is liquid or solid under ordinary conditions.

  4. The vaporized form of a medicinal preparation to be administered by inhalation.

  5. A mixture of a vapor and air, as an explosive mixture of gasoline and air burned in an internal-combustion engine.

  6. vapors Exhalations within an organ, especially the stomach, supposed to affect the mental or physical condition. No longer in technical use.

  7. vapors A nervous disorder such as depression or hysteria. No longer in technical use.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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vapor in Science
  1. The gaseous state of a substance that is normally liquid or solid at room temperature, such as water that has evaporated into the air. See more at vapor pressure, See also water vapor.

  2. A faintly visible suspension of fine particles of matter in the air, as mist, fumes, or smoke.

  3. A mixture of fine droplets of a substance and air, as the fuel mixture of an internal-combustion engine.

vaporize verb
Our Living Language  : The words vapor and steam usually call to mind a fine mist, such as that in the jet of water droplets near the spout of a boiling teakettle or in a bathroom after a shower. Vapor and steam, however, refer to the gaseous state of a substance. The fumes that arise when volatile substances such as alcohol and gasoline evaporate, for example, are vapors. The visible stream of water droplets rushing out of a teakettle spout is not steam. As the gaseous state of water heated past its boiling point, steam is invisible. Usually, there is a space of an inch or two between the spout and the beginning of the stream of droplets. This space contains steam. The steam loses its heat to the surrounding air, then falls below the boiling point and condenses in the air as water droplets. All liquids and solids give off vapors consisting of molecules that have evaporated from the substance. In a closed system, the vapor pressure of these molecules reaches an equilibrium at which the substance evaporates from the liquid (or solid) and recondenses on it in equal amounts.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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