Is it ensure, insure, or assure?
1520s, from hand + kerchief "cloth for covering the head." Thus it is a one-word contradiction in terms. By-form handkercher was in use 16c.-19c. A dropped handkerchief as a token of flirtation or courtship is attested by mid-18c.
Only once in Authorized Version (Acts 19:12). The Greek word (sudarion) so rendered means properly "a sweat-cloth." It is rendered "napkin" in John 11:44; 20:7; Luke 19:20.