CCC 2539 Envy is a capital sin. It refers to the sadness at the sight of another’s goods and the immoderate desire to acquire them for oneself, even unjustly. When it wishes grave harm to a neighbor it is a mortal sin:
St. Augustine saw envy as “the diabolical sin.”1 “From envy are born hatred, detraction, calumny, joy caused by the misfortune of a neighbor, and displeasure caused by his prosperity.”2
1 Cf. St. Augustine, De catechizandis rudibus 4, 8 PL 40, 315-316.
2 St. Gregory the Great Moralia in Job 31, 45: PL 76, 621.