“Endemic” is not a noun (usually)
“Pandemic” and “epidemic” are principally nouns, even though they can be used adjectivally, just like any other noun: e.g. “car horn.” (I say “used adjectivally” rather than “adjectives” because some linguists would argue that “car horn” is just a single compound noun [like German Autohupe], not an adjective plus a noun. Either way, “car” specifies…