laxative, 
purgative, cathartic, emetic 
elimination, 
removal, eradication, expulsion, ridding, housecleaning (US, informal), 
shakeup  
get 
rid of, eliminate, remove, eradicate, do away with, expel, expunge, 
liquidate, oust, dismiss 
pardon, 
exonerate, absolve, forgive, excuse, shrive, atone for (formal)
antonym: castigate 
(formal)
 
wash 
out, cleanse, clean, flush out, clean up, purify, sluice