1. Laziness or indifference in religious matters or spiritual apathy or boredom in the practice of virtue: "A sense of acedia came over him every time Clifton had to attend church which has been personified as one of the deadly sins."
2. A mental syndrome, consisting of listlessness, carelessness, apathy, and melancholia (extreme depression): "The patient was suffering from indifference, torpor, and sluggish mental processes."
3. Etymology: from Late Latin, from Greek akedeia, indifference; a-, "no, not" + kedos, "care, concern".