Catechism of the Catholic Church §2733 — excerpt
Another temptation, to which presumption opens the gate, is acedia. the spiritual writers understand by this a form of depression due to lax ascetical practice, decreasing vigilance, carelessness of heart.
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.