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

Earth's atmosphere is mostly nitrogen, which is heavier than water vapor.

From Science Daily • May 21, 2026

The UV radiation generated by this process can break apart water vapor molecules, leading to the formation of hydroxyl.

From Science Daily • Apr. 21, 2026

Catalytic converters turn toxic gases into water vapor and carbon dioxide, making car exhaust fumes less environmentally damaging.

From Los Angeles Times • Apr. 3, 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

I listen for a while, recognizing some words from Understanding Our Universe—evaporation, pressure, water vapor.

From "The Queen of Water" by Laura Resau