Tetraphobia
Tetraphobia (from Greek τετράς—tetras, "four" and φόβος—phobos, "fear") is the practice of avoiding instances of the number 4. It is a superstition most common in East Asian nations.
The Chinese word for four (, pinyin: sì, jyutping: sei3), sounds quite similar to the word for death (, pinyin: sǐ, jyutping: sei2), in many varieties of Chinese. Similarly, the Sino-Japanese, Sino-Korean, and Sino-Vietnamese words for four, shi (し, Japanese), and sa (사, Korean), sound similar or identical to death in each language (see Korean numerals, Japanese numerals, Vietnamese numerals).
Special care may be taken to avoid occurrences or reminders of the number 4 during everyday life, especially during festive holidays, or when a family member is ill. Just mentioning the number 4 around a sick relative is strongly avoided. Giving four of something is strongly discouraged, and a popular idiom states that "you don’t do things in fours…". Elevators in Asia and Asian neighborhoods will often skip the 4th floor or any floor whose number contains the digit "4" (as 14, 24, etc.). Military aircraft and ships will also avoid the number 4 (such as the South Korean and Taiwanese navies) due to its extreme negative connotations of death. April 4 is also considered an exceptionally unlucky day (much like Friday the 13th in the West).
Similarly, 14, 24, 42, etc. are also to be avoided due to the presence of the digit 4 in these numbers. In these countries, these floor numbers are often skipped in buildings, ranging from hotels to offices to apartments, as well as hospitals. Table number 4, 14, 24, 42, etc. are also often left out in wedding dinners or other social gatherings in these countries. In many residential complexes, building block 4, 14, 24 etc. are either omitted or replaced with block 3A, 13A, and 23A. Hospitals are of grave concern and the number 4 is regularly avoided altogether. Tetraphobia can dictate property prices. Neighborhoods have removed four from their street names and become more profitable as a result. In the same way, buildings with multiple fours can suffer price cuts of up to $30,000-$50,000. Four is also avoided in phone numbers, security numbers, business cards, addresses, ID numbers, and other numbers and are considered severe as they are personally attached to the person. Giving such numbers to Asian persons is considered extremely offensive and even grounds for law enforcement involvement or legal retaliation due to it being easily seen as a death threat and has been used as such by gangs, organised crime groups, and murderers.
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