While it acts as a modifier (like an adjective) to show ownership or possession, it still maintains its core function as a noun, representing a person, place, thing, or idea.
Here's why:
* It still represents a noun: "The dog's bone" - "dog" is the noun representing the owner.
* It can be replaced by a pronoun: "The dog's bone" can be rewritten as "Its bone".
Therefore, possessive nouns are simply nouns in a specific grammatical form indicating possession.