真的有泡
這一組就是核心畫面本身，沒有比喻成分。
adjective · B2
Covered in, or full of, a thick layer of small bubbles, the way milk, coffee, soap or seawater looks after it has been whipped, shaken or stirred hard.
起泡的、有泡沫的
核心畫面
You can hold one picture for the whole of frothy: a thick layer of tiny bubbles sitting on top of a liquid. It fills a lot of space, it is mostly air, and it does not last. Every other use keeps some part of that picture. Take away the weight and you get a story that is fun and gone by morning. Take away the value and you get a price that has been pumped up with air.
frothy 可以想成一杯液體上面那層細細密密的泡。它佔掉很大的體積，裡面幾乎都是空氣，而且撐不久。後面的用法都還帶…更多收起
frothy 可以想成一杯液體上面那層細細密密的泡。它佔掉很大的體積，裡面幾乎都是空氣，而且撐不久。後面的用法都還帶著這張圖的一部分。把「重量」抽掉，就變成好看卻沒份量的故事；把「價值」抽掉，就變成被空氣撐高的價格。所以一個字看起來跳很遠，其實一直站在同一杯泡上面。From the word’s history
Wiktionary gives the formation plainly: frothy is froth plus the ending -y, which turns a noun into an adjective meaning full of that thing. So the literal reading, full of froth, is the oldest layer, and the other two uses are that same picture moved onto books and onto prices.
維基詞典把構詞講得很清楚：frothy 就是 froth（泡沫）加上 -y（有…的、充滿…的）。所以字面上的「滿是泡沫」是最底層的意思，另外兩個用法都是同一張圖被搬到作品和價格上。這裡是構詞，不是猜測，可以放心當成事實講。
Wiktionary 'frothy' (kaikki extract): etymology tree English froth + English -y (via Middle English -y, Old English -iġ).
Three branches
像泡一樣沒重量
從核心畫面裡抽出「幾乎沒有重量」這一點，搬到看的、讀的、聽的東西上。
adjective · C1
Used about a book, film, song, show or piece of talk that is light and easy to enjoy but has no serious ideas in it, and is easy to forget afterwards.
輕鬆而沒份量的
像泡一樣被空氣撐大
從核心畫面裡抽出「看起來很滿，其實是空氣」這一點，搬到價格上。
adjective · C1
Used in business writing about a market in which prices are rising fast and have climbed above what the things are really worth, so the rise looks risky.
（市場）過熱、有泡沫的