Catechism of the Catholic Church §2484 — excerpt
The gravity of a lie is measured against the nature of the truth it deforms, the circumstances, the intentions of the one who lies, and the harm suffered by its victims.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.