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A card game, usually played for money, in which you try to get cards adding up to twenty-one — but not over. Go over and you lose at once. That risk of one card too many is the whole pleasure of the game. In casinos this game is normally called blackjack, and 'twenty-one' is the older, plainer name people use at home, at family gatherings, or in older films. Some people also say pontoon in Britain, for a home version with slightly different rules. As a card game the word takes no 'the' — you play twenty-one, not 'the twenty-one'.
二十一點（撲克牌賭博遊戲；賭場裡多稱「21點」或 blackjack）
組成twenty + one — named for the target number of the game.
原始詞典資料3 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
twenty-onenum/ˌtwɛntiˈwʌn/
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The cardinal number occurring after twenty and before twenty-two, represented in Roman numerals as XXI and in Arabic numerals as 21.
twenty-onenoun/ˌtwɛntiˈwʌn/
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card-gamesgamesBlackjack.
- They were to spend many an evening together sitting round the old kitchen table playing twentyone ….
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hobbieslifestylesportsA basketball-based game in which players attempt to score exactly twenty-one points.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。