early 15c., "a cleansing from impurity," from L. expurgationem, from expurgare "cleanse out, purify," from ex- "out" + purgare "to purge." Sense of "remove objectionable passages from a literary work" first recorded in English 1670s.
1620s, from L. expurgatus, pp. of expurgare "to cleanse out" (see expurgation). Related: Expurgated; expurgating. The earlier verb was simply expurge (late 15c.), from M.Fr. expurger.