A guinea was a gold coin used in England from 1663 to 1816, worth one pound and one shilling (21 shillings total). The coin got its name because it was originally made from gold imported from Guinea, a region in West Africa.

Though guineas haven't been minted for over 200 years, the British still sometimes use the term for pricing luxury items. When an auction house lists a painting at “500 guineas,” they mean 500 pounds plus 5% (since a guinea was worth 5% more than a pound). This tradition makes items sound more prestigious and exclusive.

The word also refers to the country of Guinea in West Africa, as well as Papua New Guinea and Guinea-Bissau.

You might also encounter guinea pig, which refers both to the small, furry pet (actually from South America, not Guinea) and to someone used as a test subject in an experiment. When scientists try a new medicine, the first volunteers are sometimes called guinea pigs.