porosity

First recorded in 1350–1400; Middle English porosytee, from Medieval Latin porōsitās ; see origin at porous, -ity

Porosity, “the state or quality of being porous or full of pores,” comes via Middle French and Old French porosité, porrosité from Medieval Latin porositās (stem porositāt- ), a derivative of the Medieval Latin adjective porōsus “porous,” itself a derivative of Late Latin porus “a passage, a channel in the body, an air passage.”
Porus is a borrowing of Greek póros “passage, ford, means, way out,” from the Proto-Indo-European root per-, por- (with other variants) “to lead, pass, pass over,” from which Latin derives portus “harbor” (from the sense “passage”) and portāre “to carry.” Proto-Indo-European por- becomes far- in Germanic, forming the verb faran “to wander,” Old English faran “to go, proceed, travel” (English fare ). From far-, Germanic also forms the verb farjan, Old English ferian “to carry, convey, transport” (English ferry ).
Both porous and porosity first appeared in a 14th-century English translation of a Latin encyclopedia of the sciences, an influential work that was written in the mid-13th century. The reference was to the tongue, described as being “porous and spongy.”