1620s, "to purge" (in anatomy), back-formation from expurgation or from Latin expurgatus, past participle of expurgare "to cleanse out, purge, purify." Related: Expurgated; expurgating. The earlier verb was simply expurge (late 15c.), from Middle French expurger. Meaning "remove (something offensive or erroneous) from" is from 1670s.