Spirits can be quite tangible, I'm proof enough of that.

[His wings rustle behind him]

My world has two definitions of 'demon' depending on the culture you're looking at. The Western world classifies them as creatures of pure evil that prey on humans in an effort to tempt them toward wickedness.

My own culture uses the word for a large variety of beings that does include some malicious creatures, but also has a number of benevolent ones. My own favorites tend to be the benign tricksters.