Hey, we know the answer to this one! Obituary is a noun. But, and here’s where things get interesting, it can also be an adjective. For example: The obituary page is the most popular section of the local newspaper. In that usage, it’s an adjective. But in this sentence, it’s a noun: I wrote an obituary for my dear grandpa.
Thank you, Grandma Maxine, for all those English lessons!