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 existance; 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: Star Trek IV: The Voyage Home)
Of all the alien races in the explored galaxy, greed (and wealth) is the driving force for all Ferengi aspects of life. (DS9 episode: "Prophet Motive")
Greed is one of the negative emotions stimulated by the low-energy waves of certain harmonic diamonds. (TNG comic: Captain's Pleasure)