Eternal sin
Thomas Aquinas lists, or has responded to, six sins that supposedly go against the Holy Spirit:
Thomas Aquinas explains that the unforgivability of blasphemy against the Holy Spirit means that it removes the entrance to these means of salvation; however, it cannot hinder God in taking away this obstacle by way of a miracle.
Christian views on sin
Mortal sins, which are any severe and intentional actions that directly disobey God, are often confused with the seven deadly sins, which are pride, envy, wrath, sloth, greed, gluttony, and lust. They are not, however, the same. The seven deadly sins are called "deadly" because they might lead another to commit other sins. Some forms of the seven deadly sins (i.e. debilitating one's health because of their love of food) can constitute as grave matter, while others may just be venal (i.e. over-eating).