Acedia is a state of apathy or dissatisfaction with one's life. Ever felt so sluggish and indifferent that you just couldn't bring yourself to care about anything? That heavy feeling is sometimes called acedia.
The word acedia comes from the Greek akēdia, meaning "lack of care" or "negligence." Fourth-century monks called it the "Noonday Demon," related to intense boredom, restlessness, and a desire to abandon one's spiritual vocation. Historically, acedia was associated with one of the "seven deadly sins," sloth — though referring to something much deeper than just physical laziness. In more modern contexts, acedia may describe any overwhelming feeling of existential emptiness or purposelessness.