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. == Rationale == The Chinese word for four (四, pinyin: sì, jyutping: sei3), sounds quite similar to the word for death (死, 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...