水面下的那股水
這一組就是畫面本身，字面上的那股水。它是這個字最早、最具體的用法。
noun · B2
A flow of water moving below the surface of the sea, a lake or a river, often in a different direction from the water on top, and often strong enough to be dangerous to swimmers.
暗流
核心畫面
Stand at the edge of the sea. The surface is flat and looks safe, but underneath it a body of water is moving steadily, sometimes the opposite way from the . You cannot see it. You only find out it is there by feeling it, and often only after it has already moved you. Both meanings of the word live inside that one picture: the water itself, and the feeling that keeps moving through a group of people while the surface stays polite.
可以想成站在岸邊看海。海面平平的，看起來沒事。可是水面底下有一股水一直在走，方向有時候還跟表面的浪相反。你看不到它。…更多收起
可以想成站在岸邊看海。海面平平的，看起來沒事。可是水面底下有一股水一直在走，方向有時候還跟表面的浪相反。你看不到它。要靠感覺，而且常常是已經被帶走了才知道。undercurrent 的兩個意思都在這個畫面裡：一個是真的那股水，一個是人群裡那股沒說出口、卻一直在動的情緒。From the word’s history
The packet's Wiktionary entry gives the word as under- + current, so the shape of the word is the picture itself: the current that is under. English later used the same shape for feelings.
評估資料裡的 Wiktionary 記的是 under- 加 current。這個字的組成本身就是那個畫面：在底下的那股水流。後來英文把同樣的組合拿去講情緒。
Wiktionary etymology supplied in this evidence packet (source_ref kaikki:3f6f69a190036ae4:1046638274), text: 'From under- + current.'
Two branches
檯面下的那股情緒
把同一個畫面搬到人身上：表面是客氣的對話，底下是沒有說出口、卻一直在流動的情緒。這是比喻的用法，Wiktionary 也把它標成 figuratively。
noun · C1
A feeling that people have but do not say out loud, especially anger or unhappiness, which you can still notice underneath the calm or polite way they are behaving.
暗藏的情緒