Is it ensure, insure, or assure?
early 15c., "a cleansing from impurity," from Latin expurgationem (nominative expurgatio), noun of action from past participle stem of expurgare "to cleanse out, purge, purify," from ex- "out" (see ex-) + purgare "to purge" (see purge). Sense of "remove objectionable passages from a literary work" first recorded in English 1610s.
1620s, back-formation from expurgation or from Latin expurgatus, past participle of expurgare "to cleanse out, purge, purify" (see expurgation). Related: Expurgated; expurgating. The earlier verb was simply expurge (late 15c.), from Middle French expurger.
To clean up, remove impurities. An expurgated edition of a book has had offensive words or descriptions changed or removed.