Is it ensure, insure, or assure?
late 14c., from Old French establiss-, present participle stem of establir (12c., Modern French établir) "cause to stand still, establish, stipulate, set up, erect, build," from Latin stabilire "make stable," from stabilis "stable" (see stable (adj.)).
For initial e-, see especial. Related: Established; establishing. An established church or religion is one sanctioned by the state.