An animal like a mosquito or leech that feeds on blood, or a person who exploits others financially or emotionally.
From English 'blood' + 'sucker' (something that sucks). Originally literal (describing leeches and mosquitoes), the metaphorical meaning of an exploitative person emerged in the 19th century.
Leeches were actually used in medicine for centuries to treat everything from headaches to infections, and modern surgeons still use them to restore blood flow to reattached fingers—bloodsuckers went from villain to hero in medical science.
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