1
: diffused matter (such as smoke or fog) suspended floating in the air and impairing its transparency
2
a
: a substance in the gaseous state as distinguished from the liquid or solid state
b
: a substance (such as gasoline, alcohol, mercury, or benzoin) vaporized for industrial, therapeutic, or military uses
also
: a mixture (such as the explosive mixture in an internal combustion engine) of such a vapor with air
3
a
: something unsubstantial or transitory : phantasm
b
: a foolish or fanciful idea
4
vapors plural
a
archaic
: exhalations of bodily organs (such as the stomach) held to affect the physical or mental condition
b
: a depressed or hysterical nervous condition
vapored; vaporing
ˈvā-p(ə-)riŋ 
1
a
: to rise or pass off in vapor
b
: to emit vapor
2
: to indulge in bragging, blustering, or idle talk
Did you know?
Speakers of the English language, mindful of the lightness and unsubstantiality of floating air and gas, have put several airy words to good use over the years to describe the act of talking idly or boastfully. The earliest such word is blow (as in "he kept blowing about his new job"), which drifted into English sometime about 1400. Vapor wafted into the language in the 1620s, and a little over 200 years later windbags, later also known as gasbags, not only blew and vapored but also gassed about anything they could.
Examples of vapor in a Sentence
Verb
a faded Southern belle tiresomely vaporing about all the handsome beaux she had in her long-ago youth
Recent Examples on the Web
Keith Cooper, Space.com, 17 June 2025
The clouds occur when air rushes up the volcanoes' slopes, cooling and condensing into visible vapor, and are particularly dense when Mars is at aphelion—the farthest point along its orbit from the Sun.
—Margherita Bassi, Smithsonian Magazine, 9 June 2025
Patrick McGeehan, New York Times, 2 Apr. 2024
Nasal decongestant vapor inhaler: A nasal inhaler is a decongestant formula used to inhale for relief.
—Daley Quinn, Health, 26 Apr. 2024
See All Example Sentences for vapor
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Noun
The analysis showed that the glass beads are coated in a layer less than 100 nanometers thick, deposited on the beads as vapor condensed out of the volcanic clouds.
—Keith Cooper, Space.com, 17 June 2025
The clouds occur when air rushes up the volcanoes' slopes, cooling and condensing into visible vapor, and are particularly dense when Mars is at aphelion—the farthest point along its orbit from the Sun.
—Margherita Bassi, Smithsonian Magazine, 9 June 2025
Verb
Scorching flames turn it to vapor and keep heating that steam to more than 400 degrees Fahrenheit before sending it out around Manhattan.
—Patrick McGeehan, New York Times, 2 Apr. 2024
Nasal decongestant vapor inhaler: A nasal inhaler is a decongestant formula used to inhale for relief.
—Daley Quinn, Health, 26 Apr. 2024
See All Example Sentences for vapor
Cite this Entry
“Vapor.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/vapor. Accessed 1 Jul. 2025.
Copy CitationMedical Definition
vapor
noun
va·por
variants
or chiefly British vapour
1
a
: a substance in the gaseous state as distinguished from the liquid or solid state
b
: a substance (as alcohol or benzoin) vaporized for industrial, therapeutic, or military uses
2
vapors or chiefly British vapours plural
a
: exhalations of bodily organs (as the stomach) formerly held to affect the physical or mental condition
b
: a depressed or hysterical nervous condition
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