The word 'vapor' was borrowed directly from the Latin noun 'vapor', meaning steam, heat, or exhalation. This Latin term is believed to have originated from the Proto-Indo-European root weh₂p- meaning 'to give off smoke or steam', a root also linked to concepts of warmth and vaporization. The semantic journey is direct and logical, moving from the ancient concept of a visible gaseous emission, like steam or mist, to the modern scientific abstraction of any substance in the gaseous state diffused in the air. Its meaning has remained remarkably stable, focusing on the visible or physical manifestation of a substance transitioning from a liquid state.

The word 'vapor' is a simplex loanword from Latin. It does not contain separable morphemes in its modern English spelling.