開玩笑的那個人
這一組是字面上的 joker：joke 加 -er，做這件事的人。同一個行為，兩種眼光，就分出了兩個意思。
noun · B1
Someone who makes a lot of jokes and enjoys making other people laugh. It is often the person in a group who is known for doing this.
愛開玩笑的人
核心畫面
You can think of a joker as the one that is not playing by the numbers. In a deck, every card has a fixed place — a number, a suit, a king or a queen — except the one with the on it, which has no value of its own and only means what the game decides. Among people, the joker is the one who steps outside the ordinary run of the conversation to make everyone laugh. The same stepping-outside can be warm or irritating depending on who is watching, and when it is a situation rather than a person, it becomes the part nobody can calculate.
joker 可以想成「不照數字來的那一個」。一副牌從 A 排到 K，每一張都有固定的大小和花色，只有畫著小丑的那張沒…更多收起
joker 可以想成「不照數字來的那一個」。一副牌從 A 排到 K，每一張都有固定的大小和花色，只有畫著小丑的那張沒有自己的點數，它值多少完全由牌局決定。人也一樣：大家照著正常的話題走，joker 偏偏岔出一句，把場面帶到別的地方去。有趣的是，同一個「岔出去」，看的人心情不同，結果就不同——你喜歡他，他是班上的活寶；你受不了他，他就變成那個白目。而當這個字用在事情上，不在人身上時，留下來的就是最後那層意思：其他都算得出來，只有它算不出來。From the word’s history
Wiktionary records joker as joke + -er, literally 'one who jokes'. For the playing card it notes the form may instead come, by alteration, from German Jucker, which also gave the card game euchre its name — and it marks that route as only possible, not certain.
詞源資料寫的是 joke（玩笑）加 -er（做這件事的人），字面就是「開玩笑的人」。至於紙牌上的 joker，同一份資料說它「可能」是從德文 Jucker 變過來的，而 Jucker 也是牌戲 euchre 名字的來源。這條線索本身就標著「可能」，所以這裡照樣寫成可能，不當成定論。
Wiktionary, entry 'joker' (noun), etymology field supplied in packet; source_ref kaikki:3f6f69a190036ae4:441617369
Two branches
牌桌上那張沒有點數的牌
這一組全部從那張畫著小丑的牌長出來。它跟頂層畫面連得很緊：一副牌裡唯一不照數字來的那張。
noun · B1
A playing card with a picture of a jester on it. It has no fixed value of its own, and only some card games use it, often as a card that can stand for any other card you need.
鬼牌／小丑牌