How would you define the relation between (for example) "Italian" and "languages"?

Solution 1:

How about category and subcategory?

Solution 2:

The precise words for what you mean are: hyponym (to be more specific) and hypernym (to be less specific).

The typical example is: horse is a hyponym of animal.

About your language example, I would say that Italian (as a language) is a hyponym of European language, which in turn is a hyponym of language. But the relationship between Italian and verb or noun is a different one. I would say that Italian contains words (and words is a hypernym of verbs and nouns).

Solution 3:

What about hierarchies?

In OLAP terminology one can have multiple overlapping hierarchies with different relationships. This is quite flexible and comfortable approach, I daresay concept

Solution 4:

You can consider using the pairs superset/subset or branches/leaves.