Is it ensure, insure, or assure?
c.1300, claspe, "metal catch or hook used to hold things together," perhaps a metathesis of clapse, and thus from or related to Old English clyppan "clasp" (see clip (v.2)).
late 14c., from clasp (n.). Related: Clasped; clasping.
clasp (klāsp)n. A part of a removable partial denture that directly retains or stabilizes a denture.
Computer Language for AeronauticS and Programming