po·ros·i·ty \pəˈräsəd.ē, pōˈ-, pȯˈ-, -sətē, -i\noun (-es) Etymology: Medieval Latin porositat-, porositas, from porosus porous + Latin -itat-, -itas -ity 1.: the quality or state of being porous < led to porosity and cracking in the weld zone — Steel > specifically: the ratio of the volume of interstices of a material to the volume of its mass < the thimble has been made in two porosities — Journal of Research > 2.: something that is porous : a porous part or area