Yo, wassup ya'll?
May I jump in on this one? What the aforementioned Slang Dictionary fails to note is that to offer props or to dis someone come from the same root. Props is widely used in hip hop culture. It is a short form of giving someone their proper respect or propers. Earliest usage I know of is from Aretha Franklin's classic Respect, where she demands her's. Dissing on the other hand is to disrespect someone. Listen to an hour of US urban radio and I guarantee you'll hear both. I've heard it used in some songs from the UK as well.