Dictionary.com
definitions

absorptivity

[ab-sawrp-tiv-i-tee, -zawrp-]
noun Physics.
  1. the property of a body that determines the fraction of incident radiation absorbed or absorbable by the body.

Origin of absorptivity

First recorded in 1860–65; absorptive + -ity
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for absorptivity

absorptivity

noun
  1. physics a measure of the ability of a material to absorb radiation, equal to the internal absorptance of a homogeneous layer of the material under conditions in which the path of the radiation has unit length and the boundaries of the layer have no influence
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012