Daemons are the go betweens of gods and humans. Greek philosophy defines them as something akin to guides.
Demons is the Latin term meaning "of evil" and refers to beings of evil, commonly a label given to malicious spirits, but academically titles given to any god, spirit, beast or being that somehow opposed the religion or culture that labeled them an enemy or dangerous. Most religions "demonized" the gods and spirits of all neighbouring religions, especially ones they warred with. This even happened with civil war such as upper and lower Egypt.