I never knew about tetraphobia till I moved to Hong Kong. Tetraphobia is the fear of the number four. It comes from the Greek words tetras (four) and phobos (fear).
The reason Chinese people are afraid of the number 4 is because the Chinese word for four sounds very similar to the word for death.
Because of tetraphobia most apartment buildings in Hong Kong do not have a fourth floor. In one building where we lived we were on the 15th floor but really it was only the 12th floor, since there was no fourth floor or fourteenth floor. Because many Western people lived in our building the managers in deference to them, had also omitted floor 13 since in western cultures the number 13 is considered unlucky.
So our apartment was on the 15th floor but it was only 12 levels up from the lobby. Confusing? It really wasn’t.