What is the correct term for the viewing hole in a door?
Solution 1:
We had one on the door when I was growing up in the 1960s London and we called it the Vassi. Just checked with my sister and she remembers the same word. Never knew why until I read Hans Adler comment. It was clearly a corruption of vasistas. It was my Grandmother's word as it was her house.
Solution 2:
I'm fine about being wrong but will add I was referring to an opening in the door which Gran called a Vassi. It was a small window that could be opened from the inside to allow delivery of small packages. I think I may have misunderstood the original question.