Wiktionary
n. (context physics English) A property of a dielectric medium that determines the forces that electric charges placed in the medium exert on each other.
Wikipedia
In electromagnetism, permittivity or absolute permittivity is the measure of resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how much electric field (more correctly, flux) is 'generated' per unit charge in that medium. More electric flux exists in a medium with a low permittivity (per unit charge) because of polarization effects. Permittivity is directly related to electric susceptibility, which is a measure of how easily a dielectric polarizes in response to an electric field. Thus, permittivity relates to a material's ability to resist an electric field (while, unfortunately, the word stem "permit" suggests the inverse quantity).
In SI units, permittivity ε is measured in farads per meter (F/m or F·m); electric susceptibility χ is dimensionless. They are related to each other through
ɛ = ɛɛ = (1 + χ)ɛ
where ε is the relative permittivity of the material, and ε = 8.8541878176.. × 10 F/m is the vacuum permittivity.
Usage examples of "permittivity".
For the metals they were the same, or nearly the same, as before, but the resistivity and permittivity of insulators had changed measurably—they had become slightly better conductors.