vapor
Americannoun
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a visible exhalation, such as fog, mist, steam, smoke, or noxious gas, diffused through or suspended in the air.
The vapors rising from the bogs smelled muddy.
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Physics. a gas at a temperature below its critical temperature.
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a substance converted into a gaseous state for technical or medicinal uses.
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a combination of gaseous particles of a substance and air.
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Archaic. vapors,
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harmful exhalations formerly supposed to be produced within the body, especially in the stomach.
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mental or physical illness, such as depression or hypochondria, formerly supposed to result from such exhalations, especially in women.
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Often Facetious. the vapors. a feeling of being overwhelmed with strong emotion.
That guy gives the press the vapors every time he announces a new project.
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Archaic.
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a strange, senseless, or fantastic notion.
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something insubstantial or transitory.
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verb (used with object)
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to cause to rise or pass off in, or as if in, vapor; vaporize.
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Archaic. to affect with the vapors; depress.
verb (used without object)
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to rise or pass off in the form of vapor.
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to emit vapor or exhalations.
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to talk or act grandiloquently, pompously, or boastfully; bluster.
noun
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The gaseous state of a substance that is normally liquid or solid at room temperature, such as water that has evaporated into the air.
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See more at vapor pressure See also water vapor
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A faintly visible suspension of fine particles of matter in the air, as mist, fumes, or smoke.
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A mixture of fine droplets of a substance and air, as the fuel mixture of an internal-combustion engine.
Usage
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.
Other Word Forms
Derived Forms
Conjugated Forms
Present
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has vaporedperfect 3rd person singular
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have vaporedperfect
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has been vaporingperfect progressive 3rd person singular
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have been vaporingperfect progressive
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is vaporingprogressive 3rd person singular
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are vaporingprogressive
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am vaporingprogressive 1st person singular
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vaporssingular 3rd person
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vaporingparticiple
Past
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had vaporedperfect
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were vaporingprogressive plural
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had been vaporingperfect progressive
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vaporedsimple
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was vaporingprogressive singular
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vaporedparticiple
Future
Etymology
Origin of vapor
First recorded in 1325–75; Middle English vapour, from Latin vapor “steam,” of uncertain origin; akin to vapidus vapid ( def. ) and vappa “wine that has gone flat”; perhaps cognate with Greek kapnós “smoke” ( see acapnia ( def. ))
Explanation
When something that is normally liquid — like water — becomes a visible, gas-like substance floating in the air, it's a vapor. The fog that often settles across your town in the mornings is one kind of vapor. Mist is also a vapor, as is your frozen breath when you can see it on a cold winter day. The Latin root word is vaporem, "exhalation, steam, or heat."
Vocabulary lists containing vapor
The Water Cycle - Introductory
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Earth Science - Middle School
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The Water Cycle - Middle School and High School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Walking through the space, I passed between the steam room and saunas of the traditional vapor and infrared variety.
From The Wall Street Journal • Jun. 9, 2026
The resulting vapor then traveled through a tube in which temperatures could be carefully controlled as the material cooled.
From Science Daily • Jun. 3, 2026
The emergency started Thursday, when the fire department responded to a vapor leak from a 34,000-gallon tank at a Garden Grove, Calif., plant belonging to GKN Aerospace, a British maker of jet parts.
From The Wall Street Journal • May 23, 2026
"If it does explode and there is a vapor, you are all safe as long as you are out of the zone that was determined to be an evacuation zone," she said.
From Barron's • May 23, 2026
Dogs barked; a couple of bats hunted moths around Harlan Betchel’s mercury vapor security lamp; the evening pulsed gently like a calm heart.
From "The Milagro Beanfield War" by John Nichols
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
