Withney's umbrella
Withney was a mathematician who divided his time between mathematics and a profession as a tightrope walker in a circus. One day, challenged by his director to invent an umbrella with only two ribs, he created this object, which he started using in his
. He unfortunately died a few years later when he fell onto the crowd.
Some mathematicians, somewhat embarrassed to have a circus artist among them, later preferred to impose the term "cusp" (in English "cusp")