from
The Collaborative International Dictionary of English v.0.48
Vapor pressure \Vapor pressure\ or Vapor tension \Vapor tension\
. (Physics)
The pressure or tension of a confined body of vapor of a
chemical substance in equilibrium with the solid or liquid
form of the substance. The pressure of a given saturated
vapor is a function of the temperature only, and may be
measured by introducing a small quantity of the substance
into a barometer and noting the depression of the column of
mercury.
[Webster 1913 Suppl. +PJC]