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." "From envy are born hatred, detraction, calumny, joy caused by the misfortune of a neighbor, and displeasure caused by his prosperity."
Source: Catechism of the Catholic Church (Vatican.va)