Witch hunt based on lie under oath: say that's not right (5)
I believe the answer is:
purge
'witch hunt' is the definition.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for purge that I've seen before include "Purify from sin or guilt" , "empty bowels" , "Removal by cleansing" , "elimination of opponents" , "Remove by cleansing" .)