"bleaching room for sugar," where it is put to drain off its molasses and imperfections, 1847, from French purgerie (1838), from purger "to wash, clean; refine, purify" (see purge (v.)). For the legal word, see perjury.
c. 1300, purgen, "clear of a charge or suspicion," from Anglo-French purger, Old French purgier "wash, clean; refine, purify" morally or physically (12c., Modern French purger) and directly from Latin purgare "cleanse, make clean; purify," especially in reference to the body, "free from what is superfluous; remove, clear away," but also figuratively "refute, justify, vindicate," from Old Latin purigare, from purus "pure" (see pure) + root of agere "to set in motion, drive; to do, perform" (from PIE root *ag- "to drive, draw out or forth, move").
By mid-14c. as "to cleanse (a person or soul) from sin or moral defilement; to cleanse, clear, purify" (metal, etc.), also medicinally "to cleanse the body or digestive tract by a laxative, diuretic, or emetic." The figurative sense of "make ideal or pure, rid of objectionable elements or members" is by 1580s. Related: Purged; purging. The Latin verb is also the source of Spanish purgar, Italian purgare.
late 14c., perjurie, in law, "the act of swearing to a statement known to be false, willful utterance of false testimony under oath," via Anglo-French perjurie (late 13c.) and Old French parjure "perjury, false witness," both from Latin periurium "a false oath," from periurare "swear falsely," from per "away, entirely" (see per) + iurare "to swear" (see jury (n.)). Related: Perjurious.