Envy is an emotion, a feeling of discontent over someone else's fortune.
Admiral Kirk told Captain Decker how envious he was of the latter's command over the newly refitted USS Enterprise. (TOS movie: The Motion Picture)
Lore described the fear felt by the colonists of Omicron Theta as envy to his near-human qualities. (TNG episode: "Datalore")
Envy is one of the negative emotions stimulated by the low-energy waves of certain harmonic diamonds. (TNG comic: "Captain's Pleasure")