An unknown or unidentified illness, often a rash. I think you better get that creeping crud checked out by a doctor—it's not looking so good.
1. n. any unidentified disease. There is some kind of creeping-crud between my toes.
2. n. a repellent person. Willy has become such a creeping-crud since he inherited all that money.
3. n. any nasty, slimy substance. That’s not creeping-crud! That’s pecan pie!