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thermal conductivity. n. 1. (General Physics) a measure of the ability of a substance to conduct heat, determined by the rate of heat flow normally through an area in the substance divided by the area and by minus the component of the temperature gradient in the direction of flow: measured in watts per metre per kelvin.
Definition of condition for English Language Learners. : 1  a way of living or existing. : 2  the state in which something exists : the physical state of something. : 3  the physical or mental state of a person or animal.