thanks for your reply! I already discovered Priberam, and at first I was very excited about it, but I have to say for some of the verbs I want to know about it just posts synonyms, as you say. The actual descriptions are often quite short, such as the one for cair: Dar queda, ir a terra.
So my impression was that this is not enough for me... and I decided to post here.
Indeed, definitions are often not universal! Also with respect to stars as you say, in which case fall would mean something like 'moving towards the earth while burning in the atmosphere'. But also with respect to different languages. Fall probably has a distinct manner component for English speakers, i.e. their interpretation is that the action that occurs is movement downwards, without support, quite possibly not voluntary, and in case of humans with sprawling arms and legs. However, this is probably not the case for Portuguese speakers... And that is exactly the kind of thing that I am interested in
Hope there is someone out there!