Authors using arabesque and grotesque?

i'm studing edgar allan poe in my cp lit cl and we're discussing his use of arabesque and grotesque. i was just wondering why people use ara. and grot. to describe the same thing? is it just to create a bigger contrast in their descriptions and to show the double-sidedness of some situations and objects? if you have a better way of describing it for me to more easily understand it please let me know!