Why not? There's a movie coming out and all.
Angels (n) - Celestial beings, servants of God. From the Greek angelos, meaning messenger. Archangel adds the Greek prefix arkh-, meaning chief or leader.
Demons (n) - Evil spirits. Again from Greek, daemon meaning a lesser god.
It is one of the oddities of modern religion that so many people who profess to being monotheists (the One True God) also believe in angels and demons. Yet, by definition all of these angels and demons are gods and demigods in their own right. Lesser gods, certainly, although Lucifer appears to be God's equal as they have fought to a draw these many millennia.