directus ad perpendiculum, or simply directus (opposed to pronus, or pronus ac f’astigatus): ☞ perpendicularis only in later writers: to be perpendicular, directum esse, or simply esse ad perpendiculum. A perpendicular line, linea, quae cathetus dicitur or cathetus only (ἡ κάθετος, sc. γραμμή). To let fall a perpendicular. lineam, quap cathetus dicitur, demittere in (with ablative).