Greed is an emotion, an excessive level of desire for something.
Harry Mudd's greedy, human nature-observed by Norman-was the hindrance to his continued existence; without android supervision by himself and others of his world. (TOS episode: "I, Mudd")
Avarice was another word for the strong, selfish desire. Dr. Nichols was promised to be rich beyond his dreams (unknowingly given matrice dynamics from "future" technology) in exchange for donating his Plexiglas, no questions asked. (TOS movie: The Voyage Home)
Greed (and wealth) was the driving force for all Ferengi aspects of life. (DS9 episode: "Prophet Motive")
Greed was one of the negative emotions stimulated by the low-energy waves of certain harmonic diamonds. (TNG comic: "Captain's Pleasure")