This is a bit of a digression, I had intended to write about biomedicine and epidemiology next, but I decided to insert something else.
First, I'll just note that dictionary definitions of science aren't really accurate or useful. This is a member of a class of problems we run into frequently here, that is arguments about the meaning of words substituting for arguments about substantive matters. I would say that the reason you won't find a good dictionary definition of science is that the concept is too complex. You can read about the difficulty of defining science here, if you are interested in academic philosophy.
Specifically, the subject matter and product of science is not limited to proven facts. Scientists deal in the full range of certainty and uncertainty, from conjectures that they consider unlikely but ought to be tested, to alternative hypotheses, to conclusions of which they feel fairly confident, to conclusions which are generally accepted and are woven into broader, widely accepted theories. Note that the word "theory" as used by scientists does not mean what it usually means in the vernacular, which is more like what scientists call a hypothesis. Rather, a theory is an explanatory model that includes numerous observations and presumed causal relationships. For example, Einstein's theory of gravity hold that mass warps space-time, such that other masses' trajectory through space-time follows the warped path.
There is a lot more to it than that but the essential point is that the theory makes numerous predictions which have been tested and found to hold true. That increases confidence in the correctness of the theory, but it will probably never be considered "proved." It's just the working theory we have now. And as I noted last time, doubts are creeping in. However, even if something else is going on, the theory is still useful for the purposes which have been established, just as Newton's theory is useful for everyday purposes.
Let us now turn to a commonly used term "conspiracy theory." People have come to use this to mean something more specific than the words taken by themselves would imply. After all, there are conspiracies, and there is nothing inherently irrational in having theories about them. Investigators and prosecutors formulate conspiracy theories all the time, and sometimes they prove them in court. I remember some years ago (before the present Q and pizzagate madness) a Big Professor publishing a study of personal characteristics associated with belief in conspiracy theories. He asked people about such theories as scientists conspiring to invent the hoax of global warming to get grant funding, the Illuminati secretly controlling global affairs, that sort of thing. One of his conspiracy theories was that drug companies conceal evidence that their products are ineffective or unsafe.
I actually wrote to him and pointed out that the latter conspiracy theory is in fact true. He scoffed. The FDA has since changed its regulations to make this more difficult, but the problem has not been eliminated. By the way, this is why Purdue Pharma is out of business and has paid billions in fines and damages.
Anyway, "conspiracy theory" now means a theory that is objectively ridiculous, generally involving powerful people somehow secretly controlling important matters or engaging in nefarious activities. However, this does actually happen. The difficulty, as with the demarcation problem, is in deciding which conspiracy theories are actually ridiculous. In some cases this should not be a problem. That prominent Democratic politicians and operatives, along with Hollywood stars, secretly run a global child sex trafficking ring and kill the children in order to extract a chemical that preserves the conspirators' youth is in that category. If you had any doubt of it before, you might reconsider since we had a Republican led administration and Department of Justice for four years and they didn't do anything about it.
But other cases are more doubtful. Did James Earl Ray act alone in killing Martin Luther King? How about Sirhan Sirhan and RFK? There is reason to doubt the accepted version of these events, but on the other hand there is no strong evidence in favor of any other versions. Where people go wrong is in feeling certain about one or another version -- deciding that they know the One True Story. Sometimes we don't, and probably never will. But some people have a hard time living with that.