from The Century Dictionary and Cyclopedia
- n. A small trap or hole in a door made for peering or watching, either from within or from without. Also judas. See judas, 3.
Sorry, no etymologies found.
Alone in a stripped room, it will be nearly impossible for him to act suitably engaged and hence nearly impossible to act sane, and so the patient may try to cover up the judas-hole in the cell door in order to prevent passers-by from transforming a private predicament into a social situation.