Picture a closed circle of people who all know each other, take orders from the same few at the top, and tell outsiders nothing. Membership is the whole point: you are either inside the circle or you are not, and the people inside look after each other first. Every use of mafia can be held next to that circle. Change what the circle controls and you change the meaning: illegal business, a profession, or, in a party game, just the secret in the room.
The source records that the word was borrowed from Italian mafia and that its further origin is uncertain; several explanations have been put forward and none is settled.
來源資料說這個字借自義大利文 mafia，再往前的來源並不確定，幾種說法都沒有定論。所以只能說它從義大利文進入英文，更早的故事先留白。
Wiktionary (kaikki extract) etymology_text for Mafia: "Borrowed from Italian mafia, of uncertain origin... the etymology remains uncertain"
Three branches
有組織的犯罪
圈子控制的是非法生意，這是這個字最原本、也最常見的一支。
noun · B2
The Mafia is a large, well organized group of criminals that began in Sicily in Italy and later became powerful in the United States too, controlling many illegal kinds of business and keeping its members silent and loyal.
黑手黨
行業裡的小圈圈
圈子還在，控制的東西換成一個行業或一間機構的決定權。這是比喻上的借用，不是說這些人犯法。
noun · B2
A small, powerful group of people inside an organization or a profession who help and protect each other and keep control of decisions. Used when the speaker thinks this is unfair.
把持圈子的小集團
派對推理遊戲
遊戲直接拿這個組織的名字來當名字，因為玩法就是「少數人知道祕密、多數人不知道」，剛好是圈內圈外的畫面。
noun · B1
A party game for a group of players. A few players are secretly given the role of the mafia, and the rest have to work out who they are by talking, asking questions and voting.
推理派對遊戲