Wall up Definition 1 of 3Pro Tip 1/3Physical Changes Used when mentioning physical modifications to a structure. The renovation plans include walling up several archways. Pro Tip 2/3Creating Boundaries Refers to making a space more private or secure. They walled up the courtyard to prevent outsiders from entering. Pro Tip 3/3Irreversible Action Indicates a permanent or semi-permanent action. Once they wall up that entrance, there's no going back.