Halliday & Matthiessen (2014: 646-7):
Repetition and synonymy are both elaborating relations based on identity; one lexical item restates another. There is a second kind of elaborating relationship – attribution. This is based on classification (specific to general): the first lexical item represents a class of thing and the second either (i) a superclass or a subclass or (ii) another class at the same level of classification. For example:
And do you know anything about mediæval literature; have you ever heard of any other kinds of literature in the mediæval period besides Chaucer?
Most limestone probably originates from organisms that remove calcium carbonate from sea water. The remains of these animals may accumulate to form the limestone directly, or they may be broken and redeposited.
Noah’s wife and his sons’ wives went to the fields to gather fruit and grain and vegetables. They would need plenty of food for themselves and the animals on the ark. The remains of these animals may accumulate to form the limestone directly, or they may be broken and redeposited.
Thus in the last example, fruit, grain and vegetables are co-hyponyms of food.