I've always referred to pre-startup ideas and the pre-revenue/early-revenue stages as "startups".
But a lot of forums and media use "startup" for what are frankly damn big businesses. e.g. today an article called Monzo a hot startup!
So is there a better word for very early stage startups?
Startup is a category, sometimes just an adjective. It takes into consideration size, age, structure, and ability to absorb change. It is not a fixed thing. That's precisely why there are more specific definitions that look at things LIKE size, age, revenue, and agility. If you're concerned about the financial state as a measure, you talk about seed, pre-revenue, etc. If you're concerned about structure you talk about flat versus hierarchical. It all depends on what you care about as to the words used to categorize these businesses. Startup is too big a category, that's why it's modified by the other terms.