blood-letting (n.)youdaoicibaDictYouDict[blood-letting 词源字典]
also bloodletting, early 13c., blod letunge, from blood (n.) + let (v.). Hyphenated from 17c., one word from mid-19c. Old English had blodlæte "blood-letting."[blood-letting etymology, blood-letting origin, 英语词源]