Not that I would ever feign understanding of those strange individuals who spend so much of their time conversing with ghosts. But ‘acedia’ seems like the kind of word that should be in this dictionary.
Please consider this a request for a new entry.
My 2¢:
Etymology: from classical Greek ἀκηδία, ἀ (privative alpha) + κῆδος (“care”, “concern”, “solicitude”) - [source]
Meaning(s): “sloth”, “indolence”, “spiritual apathy and inactivity” - [source]
Use: declared obsolete in 1933 by OED with references dating from 1520 and 1730. Then revived in mid-20th century (Aldous Huxley, Ian Fleming et al.) [source]
In the Middle Ages the lack of enthusiasm (for the tenets of the Church of Rome) implicit in the word was listed among the 7 capital sins (cf. Dante Alighieri, “La Divina Commedia”).
Nowadays it is tendentially regarded as a pathological condition treatable with pharmacological or psychological methods, a punishment considerably worse than a merciful stake burning.