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

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

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

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

From "The Queen of Water" by Laura Resau