If you describe something as nebulous, you mean that it is vague and not clearly defined or not easy to describe.
例句
The notions we children were able to form of the great world beyond were exceedingly nebulous...我们这些孩子所能形成的对外部世界的认识是非常模糊的。Music is such a nebulous thing.音乐是如此蒙之物。
英汉词典释义
adj.
朦胧的,模糊的
nebulous assurances of future cooperation对未来合作的含糊的保证
英英词典释义
Adjective
1. lacking definite form or limits;
"gropes among cloudy issues toward a feeble conclusion"- H.T.Moore"nebulous distinction between pride and conceit"
2. lacking definition or definite content;
"nebulous reasons""unfixed as were her general notions of what men ought to be"- Jane Austen