If this word sounds familiar, you’re likely better acquainted with its antonym “impervious.” “Pervious,” which predates its opposite, comes from the Latin word “pervius” (“having a passage through”). Pervious membranes are crucial for most organic, living things — humans, for example, could not survive without the permeable cells that make up our bodily systems. However, cell membranes are selectively pervious, which means that they regulate which materials and substances are allowed to enter and exit at any given time.