The seven deadly sins, more properly called the seven capital sins, are the sins to which we are most susceptible because of our fallen human nature. They are the tendencies that cause us to commit all other sins. They are called "deadly" because, if we engage in them willingly, they deprive us of sanctifying grace, the life of God in our souls.
What Are the Seven Deadly Sins?
The seven deadly sins are pride, covetousness (also known as avarice or greed), lust, anger, gluttony, envy, and sloth.
Pride: a sense of one's self-worth that is out of proportion to reality. Pride is normally counted as the first of the deadly sins, because it can and often does lead to the commission of other sins in order to feed one's pride. Taken to the extreme, pride even results in rebellion against God, through the belief that one owes all that he has accomplished to his own efforts and not at all to God's grace. Lucifer's fall from Heaven was the result of his pride; and Adam and Eve committed their sin in the Garden of Eden after Lucifer appealed to their pride.
Covetousness: the strong desire for possessions, especially for possessions that belong to another, as in the Ninth Commandment ("Thou shalt not covet thy neighbor's wife") and the Tenth Commandment ("Thou shalt not covet thy neighbor's goods"). While greed and avarice are sometime used as synonyms, they both normally refer to an overwhelming desire for things that one could legitimately possess.
Lust: a desire for sexual pleasure that is out of proportion to the good of sexual union or is directed at someone with whom one has no right to sexual union—that is, someone other than one's spouse. It is possible even to have lust toward one's spouse if one's desire for him or her is selfish rather than aimed at the deepening of the marital union.
Anger: the excessive desire to take revenge. While there is such a thing as "righteous anger," that refers to a proper response to injustice or wrongdoing. Anger as one of the deadly sins may begin with a legitimate grievance, but it escalates until it is out of proportion to the wrong done.
Gluttony: excessive desire, not for food and drink, but for the pleasure obtained by eating and drinking. While gluttony is most often associated with overeating, drunkenness is also a consequence of gluttony.
Envy: sadness at the good fortune of another, whether in possessions, success, virtues, or talents. The sadness arises from the sense that the other person does not deserve the good fortune, but you do; and especially because of a sense that the other person's good fortune has somehow deprived you of similar good fortune.
Sloth: a laziness or sluggishness when facing the effort necessary to perform a task. Sloth is sinful when one lets a necessary task go undone (or when one does it badly) because one is unwilling to make the necessary effort.