Is it ensure, insure, or assure?
1670s, as the fidget "uneasiness," later the fidgets, from a 16c. verb fidge "move restlessly," perhaps from Middle English fiken "to fidget, hasten," from Old Norse fikjask "to desire eagerly" (cf. German ficken "to move about briskly;" see fuck).
1670s (implied in fidgetting); see fidget (n.). Related: Fidgeted.