What does vapour mean?
Vapour is a British-English spelling of vapor, meaning a substance in its gaseous state. Its best-known use is water vapour: the invisible form of water in the air, which can become visible as mist or cloud when it condenses into tiny droplets. The word also appears in technical contexts such as vapour pressure and in descriptions of exhaust, breath, or aircraft trails. In everyday speech, British speakers may prefer steam or mist when they mean visible moisture, while vapour remains especially useful for referring to the gas itself. As a verb, vapour means to become vapour or give off vapour, though this use is less common than the noun. The word is valuable because it distinguishes gaseous water from the liquid droplets that people can actually see. Its British and American spellings reflect the continuing difference in spelling conventions between the two varieties of English.
A gas formed when a liquid or solid substance changes into a gaseous state, especially the invisible water vapour in the air. In everyday use, it can also refer to a cloud or mist of tiny droplets.
"The sun warmed the wet pavement, sending up clouds of vapour."
The British spelling is standard in British English; American English generally uses vapor.
To emit vapour or to become vapour.
"The water began to vapour as the temperature rose."
This use is relatively uncommon compared with the noun and is especially associated with formal or descriptive writing.
The plural is used when referring to separate samples, types, or quantities of vapour; in many scientific contexts vapour is used as a mass noun.
"The experiment compared the vapours produced by different solvents."
Water vapour is invisible: the white clouds you see are tiny liquid droplets formed when invisible vapour condenses.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does vapour come from?
The word entered English from Old French vapour or vapor, ultimately from Latin vapor, meaning steam, vapour, or exhalation. Latin forms related to vapor, including vaporis, also underlie words such as evaporate, vaporous, and vaporize. The British spelling developed with the -our ending, while American English generally uses the shorter form vapor.
Related word forms
How vapour is actually used
In British English, vapour is the standard spelling, while American English usually uses vapor. The noun is common in scientific and meteorological contexts, such as water vapour and vapour pressure. In everyday British usage it can sound formal or somewhat literary, so steam or mist may sound more natural in many situations.
Easily confused with vapour
Vapour is the standard British spelling, whereas vapor is the standard American spelling; they refer to the same word, though pronunciation may differ slightly by accent.