What is a noun that tells more about another noun?

A noun that tells more about or describes another noun is called a noun adjunct. An example of a noun adjunct is "baseball player." Sometimes, two noun adjuncts may be strung together, as in "chicken salad sandwich." In these cases, each noun modifies the next noun.

Noun adjuncts are also referred to as attributive nouns, which are nouns that modify other nouns attributively and can be removed without affecting the meaning or the grammar of the sentence; for example, “chicken soup” or "government official."

The term "adjectival noun" was once used synonymously with "noun adjunct," but recent usage reserves the term for adjectives that act as nouns.