Is it ensure, insure, or assure?
occlude oc·clude (ə-klōōd')
v. oc·clud·ed, oc·clud·ing, oc·cludes
To cause to become closed; obstruct.
To prevent the passage of.
To bring together the upper and lower teeth in proper alignment for chewing.
To enclose a virus, as in an inclusion body.
In chemistry, to absorb and retain gases and other substances.