1. The state or property of being porous.
2. A structure or part that is porous.
3. The ratio of the volume of all the pores in a material to the volume of the whole.

[Middle English porosite, from Old French, from Medieval Latin porōsitās, from porōsus, porous. See porous.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.