joker
/ˈdʒəʊkə(r)/noun
1
- a person who is fond of joking爱开玩笑的人。
1.1
- informal a foolish or inept person〈非正式〉傻瓜, 笨蛋：
a bunch of jokers.
一群笨蛋。
2
- a playing card, typically bearing the figure of a jester, used in some games as a wild card（扑克牌）大王; 小王。
3
- US a clause unobtrusively inserted in a bill or document and affecting its operation in a way not immediately apparent〈美〉伏笔, 曲笔（在法案或文件中插入的不显眼条款, 其影响实施的作用不会被立即察觉）。
词源
the joker in the pack a person or factor likely to have an unpredictable effect on events 诡秘的人（或因素），难以捉摸的人（或因素）。