Because i like correcting people here is a english lesson
say your getting a blueberry muffin
both blueberry and muffin are nouns wich are objects or something you can touch
but because you said blueberry muffin your using the noun blueberry to describe the muffin
an adjective is a word discribing a noun or verb
so your using blueberry as an adjective
so it a noun
and a adjective