Go down inside a boat, past the deck, past the cabin, until you cannot go any lower. The floor curves outward here, and whatever has leaked in over the last month is lying in it: old water, a little oil, a smell. That low curved space is the bilge. Hold on to two features of it — it is the very bottom, and what gathers there is the stuff nobody wants. Both features are still working in the word's rude second meaning.
可以想成往船裡一直往下走：過了甲板，過了船艙，走到不能再低的地方。那裡的底板往外鼓出一個弧度，這一個月漏進來的東西全躺在裡面——舊水、一點油、一股味道。那塊又低又彎的空間就是 bilge。記住它的兩個特徵：它在最底下，而且積在那裡的都是沒人要的東西。這兩點在它罵人的第二個意思裡都還在運作。
From the word’s history
The source entry says bilge is likely derived from bulge, and compares Middle English bulgen (to ground or scuttle a ship).
來源資料說 bilge 很可能來自 bulge（鼓出來），並拿中古英文的 bulgen 作比較。這正好解釋了核心畫面裡那個弧度：船底往外鼓的那一圈。同一個理由下，木桶最寬的那一圈在英文裡也叫 bilge。
Wiktionary, "bilge"
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