A brief reference, without explanation, to a person, a text, a myth or a fact known outside the work, which carries with it the meaning of that other story.
In The Slum
Jerônimo era alto, espadaúdo, construção de touro, pescoço de Hércules, punho de quebrar um coco com um murro: era a força tranquila, o pulso de chumbo, Jerônimo was tall, broad-shouldered, built like a bull, with the neck of Hercules, a fist that could crack a coconut with one punch: he was calm strength, a pulse of lead
The "neck of Hercules" calls up the hero of legendary strength and lends the phrase the prestige of a myth, without explanation, so the reader can gauge the size of the man Firmo is about to face.
Chapters X to XI: The Baron's Title, the Razor Slashing and Pombinha's Visit, the narrator