Mors immedicabilis was a dangerous disease generally referred to as the Incurable Death.
Whole planets were wiped out by Mors immedicabilis. The disease was fast spreading, causing pustules and weakness. The victim was usually dead within minutes. As the name suggested, there was no known cure for the disease. Slarn, whose could psychosomatically incubate diseases in himself, accidentally infected himself and his steward with the malady. (AUDIO: Slipback [+]Eric Saward, BBC Audio Dramas (BBC Radio 4, 1985).)