Vapour

Vapour

Noun · /ˈveɪpə/ · gas form of a substance normally liquid or solid at room temperature

Definition

Vapour is the gaseous state of a substance that is ordinarily a liquid or solid at room temperature. When water heats past boiling point, it becomes vapour. Breath visible in cold air is water vapour condensing into droplets. Vapour differs from a permanent gas: lower the temperature enough and vapour returns to liquid.

Origin

From Latin vapor — steam, heat. Entered Middle English via Old French vapour around the fourteenth century. Early physicians used the term for supposedly harmful aerial emanations rising from the earth believed to cause disease. British English retains the -our spelling; American English uses vapor.