Is it ensure, insure, or assure?
1540s, from Latin cauterium "branding iron," from Greek kauterion (see cauterize).
cautery cau·ter·y (kô'tə-rē)n.
An agent or instrument used to destroy tissue by burning, searing, cutting, or scarring, including caustic and electric currents, lasers.
The act or process of cauterizing.