A small boil or painful infected bump on the skin caused by bacteria, also known as a furuncle.
From Latin 'furunculus' meaning a petty thief or a small boil, diminutive of 'fur' (thief), because the infection was thought to 'steal' away health.
Medieval doctors thought boils were literally stealing your life force, so they named them after thieves—a perfect example of how disease was personified in ancient medicine.
Complete word intelligence in one call. Free tier — 50 lookups/day.