One way to hold this word: think of a cloud of steam instead of a box. A box has edges your finger can trace, and you can say exactly what is inside it and what is outside. Steam has none of that. You can see it is there, and you still cannot draw a line around it. Everything nebulous does — to a shape in fog, to an idea in a meeting, to a patch of light in a telescope — is that same missing edge.
可以想成一團蒸氣，而不是一個盒子。盒子有邊，手指描得出來，也講得出什麼在裡面、什麼在外面。蒸氣兩樣都沒有。你看得出它在那裡，卻圈不出它的界線。nebulous 的每個用法都在講這件事：霧裡的形體、會議上的想法、望遠鏡裡的一團亮光，共同點都是「少了那條邊」。
From the word’s history
Latin nebula meant mist or cloud, and nebulosus meant full of mist; English took the word through Middle French. The modern core image is still that mist.
拉丁文 nebula 是霧、雲，nebulosus 是「滿是霧的」，經由中古法文進入英文。今天的核心畫面其實還是那團霧，沒有走遠。
Wiktionary entry for nebulous, etymology_text supplied in this packet (kaikki:3f6f69a190036ae4:821444863)
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