Either relating to the large vein in the neck, or metaphorically, the most vulnerable point of something.
From Latin 'jugulum' (collarbone, throat), derived from 'jugum' (yoke). Medieval anatomy texts applied the term to the prominent neck veins, and by extension, the vital weak point.
When we say 'go for the jugular' we're speaking 1300-year-old anatomical truth—the jugular vein is literally the fastest way to kill something, which is why predators always attack the neck.
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