Meaning

noun closure or blockage (as of a blood vessel)

noun (meteorology) a composite front when colder air surrounds a mass of warm air and forces it aloft

noun (dentistry) the normal spatial relation of the teeth when the jaws are closed

originBorrowed from Late Latin occlūsiō, occlūsiōnis (“occluding, obstruction”), from the Classical Latin occlūdō (“to shut up or close up; to restrain”), from ob + claudō (“to shut or close”).

Etymology from Wiktionary, CC BY-SA 3.0