鍋子本身
這一支就是畫面本身，沒有比喻。先看懂這口鍋，其他用法才會從畫面裡自己長出來。
noun · C1
A strong metal pot used to heat metal until it turns to liquid, so that different metals can be mixed together or poured into a shape.
坩堝／熔鍋
核心畫面
One way to hold this word: a heavy pot over a fire, with pieces of different metal dropped into it. Each piece arrives with its own shape and its own colour. The heat takes those shapes away. What is left is one hot liquid that belongs to all of them and to none of them, and while it is still hot, it can become anything. Everything else the word does is this pot, used about something that is not metal.
這個字可以想成一口架在火上的厚鍋子。不同的金屬被丟進去，每一塊都有自己的形狀和顏色。火一燒，那些形狀就留不住了。剩下…更多收起
這個字可以想成一口架在火上的厚鍋子。不同的金屬被丟進去，每一塊都有自己的形狀和顏色。火一燒，那些形狀就留不住了。剩下的是一鍋熱液體，它屬於每一塊，又不屬於其中任何一塊。而且只要還熱著，它就還能變成任何東西。之後的每一種用法，都是把這口鍋端到別的地方去用：有時候丟進去的是人，有時候是想法，有時候是一件還沒決定的事。From the word’s history
Wiktionary's note on this entry says the expression was popularized by the British writer Israel Zangwill in his 1908 play The Melting Pot. That is a note about how the figurative use spread, not a claim about where the two ordinary words came from.
來源資料只說了一件事：這個說法之所以流行，跟英國作家 Israel Zangwill 1908 年的劇本 The Melting Pot 有關。這是在講「比喻用法怎麼傳開」，不是在講 melt 和 pot 這兩個字的字源。
Wiktionary entry for 'melting pot' (packet source_ref kaikki:3f6f69a190036ae4:1585826958:15439), etymology_text field
Three branches
丟進去混成一體的地方
把鍋子換成一個地方，把金屬換成人或想法，其他都不變：不同的東西進來，互相接觸，慢慢混成一個整體。
noun · B2
A place, usually a city or a country, where people from many different races, countries, or social classes come to live together, mix, and over time form one shared way of life.
民族熔爐
還在鍋裡，還沒成形
這一支抓的不是「混合」，而是鍋裡的另一個事實：東西還熱著、還是液體，所以還沒有固定的形狀。
noun · C1
If a plan, an idea, or someone's situation is in the melting pot, nothing about it has been settled yet, and it could still change a great deal.
還沒定案／仍可能大改