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

The season’s rainstorm brought a sky as blue as a newborn’s eyes, but water vapor is still rising from the multicolored canopies.

From Los Angeles Times • Mar. 12, 2026

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

From Barron's • Jan. 21, 2026

A familiar physical example appears at the critical point of water, defined by a precise temperature and pressure at which liquid water and water vapor become indistinguishable.

From Science Daily • Dec. 16, 2025

The high oceanic temperatures will release more water vapor into the air, increasing cloudiness, shielding the Earth from sunlight and delaying the end a little.

From "Cosmos" by Carl Sagan