There are two words on either side of the word I'm looking for: synonym and antonym. Of course, a synonym is a word that means the same thing (automobile vs. vehicle), and an antonym is a word that means the opposite (male vs. female). However, let's use the example of automobiles. There are different types: car, truck, van, SUV, etc. They're neither synonyms or antonyms of each other. But is there a word that describes their similarities, given they're all automobiles?
The word should fit this sentence:
A car is a _______________ of a truck.