water vapor

American  

noun

1. a dispersion, in air, of molecules of water, especially as produced by evaporation at ambient temperatures rather than by boiling.

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water vapor Scientific  

1. Water in its gaseous state, especially in the atmosphere and at a temperature below the boiling point. Water vapor in the atmosphere serves as the raw material for cloud and rain formation. It also helps regulate the Earth's temperature by reflecting and scattering radiation from the Sun and by absorbing the Earth's infrared radiation.

2. See also vapor

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Etymology

Origin of water vapor

First recorded in 1875–80

Example Sentences

The observations show that the planet's atmosphere is surprisingly dense and filled with heavier molecules, including water vapor, carbon dioxide, sulfur dioxide, and traces of methane.

From Science Daily • May 7, 2026

Ajami pointed out that extreme heat is not only causing snow to melt faster but is also causing sublimation, in which snow is transformed directly to water vapor.

From Los Angeles Times • Mar. 15, 2026

That storm turned water vapor into ice at natural gas wellheads, blocking fuel production.

From Barron's • Jan. 21, 2026

At the same time, a warmer atmosphere holds more water vapor, which is then released in fewer, more extreme rainstorms.

From Los Angeles Times • Jan. 9, 2026

There are small traces of nitrogen, water vapor, argon, carbon monoxide and other gases, but the only hydrocarbons or carbohydrates present are there in less than 0.1 parts per million.

From "Cosmos" by Carl Sagan