Hold one picture for sump: the lowest place, where liquid ends up because it has nowhere further to fall. A floor is , a shaft goes down, a cave dips, an engine sits above a pan, and everything wet runs to that one low spot and stays there. Every use of the word is that spot seen in a different building or machine. The word is a of swamp, which fits: both are about water standing in a low place. What changes from use to use is only what the low place is part of, and whether the liquid is there to be pumped out, to be used again, or to block your way.
From the word’s history
From Middle English sompe, from Middle Dutch or Middle Low German sump, ultimately from Proto-Germanic *sumpaz. It is a doublet of swamp.
來自中古英文 sompe，再往上是中古荷蘭文或中古低地德文的 sump，最後回到原始日耳曼語 *sumpaz。它跟 swamp 是同源分出來的兩個字，所以「水停在低窪處」這個畫面，從最早就在這個字裡面。
Wiktionary, "sump"
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