Grave Transgression in the Catholic Church

Word Meaning:

MORTAL SIN — (Roman Catholicism, theology) A sin which causes the loss of God's grace, leading to eternal damnation, unless the sinner repents, which includes their intent to confess and atone; such a sin is defined as a grave transgression against one of the Ten Commandments with the full knowledge and deliberate consent of the sinner.

Definitions from Wiktionary.