byword

tunnuslause A proverb or proverbial expression, common saying; a frequently used word or phrase.
A characteristic word or expression; a word or phrase associated with a person or group.
Someone or something that stands as an example (i.e. metonymy metonymically) for something else, by having some of that something's characteristic traits.
An object of notoriety or contempt, scorn or derision.
1890, (w), The Picture of Dorian Gray, chapter XII:

"I know you and Harry are inseparable. Surely for that reason, if for none other, you should not have made his sister's name a by-word."