A hyponym, in relation to a hypernym, is a word that describes a class that is a subset of the hypernym word. A beagle is a kind of hound, which is a kind of dog, which is a kind of carnivore, which is kind of mammal, which is ...etc, etc.
You're looking for the word which describes a class that has no hyponyms. I would call this a
because it is at the bottom (terminal) of the hierarchy. The 'root' of the tree would then be the terminal or maximal hypernym.
This is what I would call it, but never have until now because of the originality of the concept to me. I don't know if this would be all that useful since I don't think you could ever prevent coming up with a more refined hyponym or more inclusive hypernym.
As to 'proper' nouns, those for particular individuals or names of particular objects, in the same parlance as hypnyms and hypernyms, are called an
In your examples, a Ford Mondeo is an instance of a model of car, and car is a hyponym of vehicle which is a hyponym of machine, etc, etc. (yes, one could consider 'Ford Mondeo' a hyponym of car, a concept of which there are instances namely this car in this parking lot.)