Is it ensure, insure, or assure?
1580s, from Middle French bougier "to move, stir" (Modern French bouger), from Vulgar Latin *bullicare "to bubble, boil" (hence, "to be in motion"), from Latin bullire "to boil" (see boil (v.)). Cf. Spanish bullir "to move about, bustle;" Portuguese bulir "to move a thing from its place." Related: Budged; budging.