The phrase "a nebulous idea" is correct and usable in written English.
It can be used to describe an idea that is vague, unclear, or not well-defined.
Example: "The proposal was met with skepticism because it was based on a nebulous idea that lacked concrete details."
Alternatives: "an unclear concept" or "a vague notion."
In fact, it was the unease of mathematicians with such a nebulous idea that led them to develop the concept of the limit.
Since 2001, a whole shelf of books have been published about al-Qaida, and the overall consensus is that they are now no more than a brand, a nebulous idea that anyone can subscribe to.
Just as Pabst might evoke some fairy-tale notion of blue-collar, union-strong Milwaukee, so, too, does the old Miller Lite can suggest a nebulous idea about the American past — one generic enough to let young people fill in the gaps themselves.
Perhaps it is good news, then, that there is scant evidence in the panel's report of his infamous "golden thread", a nebulous idea which seeks to imply that western styles of democratic government and openness are a foundation of growth and poverty reduction.
Estes found her first meeting with Lynch "really intimidating" and had "only had a nebulous idea of what I was getting into," but she applied and was accepted as a doctoral student in Lynch's lab.
It was still a nebulous idea that wouldn't coalesce for another decade.
In this respect I'd contend that bullshit is the rhetorical plasma of democratic, civil society: I have a perhaps-decent but nebulous idea, or I'm forming an opinion on something, and I circulate it through the democratic process of debate and conversation, and grow either to refine or reject the idea.
Because the labor market finally seemed to be recovering, Mr. Kerry had shifted his criticism from the absolute number of new jobs to the broader if more nebulous idea of a "middle-class squeeze" and a declining quality of life.
He was not talking about actual extinctions, but the much more nebulous idea of an extinction threat.
On the other hand, he knew nothing of doubly periodic functions, the classical theory of quadratic forms, or Cauchy's theorem, and he had only the most nebulous idea of what constitutes a mathematical proof.
It's about time for him to stand up and just go real black for one interview and say, 'If you keep fucking with me, we gon' have problems.'" Mackie is devoted to straight-talking, which is perhaps why "this nebulous idea of celebrity" and getting lost in it is so alarming to him.
