What is a word derived from a person's name called?

A word derived from a person’s name is called an eponym. The person’s name may become the source of a common noun, verb, adjective, or other expression, often after the original individual has become associated with an invention, place, discovery, condition, or cultural idea.

Examples include “braille,” named after Louis Braille; “fahrenheit,” associated with physicist Daniel Gabriel Fahrenheit; and “pasteurization,” named after Louis Pasteur. “Boycott” comes from Charles Boycott, a 19th-century Irish land agent whose name became a verb after organized social exclusion was directed against him.

Eponym is sometimes used more broadly for something named after a person, including institutions, places, and scientific laws. That broader usage can create confusion with “toponym,” which specifically concerns a place name, and with “neologism,” which means a newly created word or expression regardless of its source. An eponym can also be a person whose name supplies the term, so the word describes both the naming relationship and, in some contexts, the resulting word.