Definition:

ferrule : the protective point or knob on the far end of an umbrella

Example Sentence:

He used his umbrella as a cane, and with every step planted its ferrule in the ground.

Origin:

Ferrule comes from the Latin viriola, meaning "small bracelet." This makes more sense when you consider that ferrule is also the term for the metal band at the end of a table leg (or similar object) that strengthens it or prevents it from splitting.