Friday the 13th occurs when the thirteenth day of a month falls on a Friday, which superstition holds to be a day of bad luck. In the Gregorian calendar, this day occurs at least once, but at most three times a year. Any month’s 13th day will fall on a Friday if the month starts on a Sunday.
The fear of Friday the 13th is called friggatriskaidekaphobia, frigga, meaning “Friday” and triskaidekaphobia, or paraskevidekatriaphobia, a word derived from the concatenation of the Greek words Paraskeví (Παρασκευή, meaning “Friday”), and dekatreís (δεκατρείς, meaning “thirteen”), attached to phobía (φοβία, from phóbos, φόβος, meaning “fear”). The word was derived in 1911 and first appeared in a mainstream source in 1953.
According to folklorists, there is no written evidence for a “Friday the 13th” superstition before the 19th century. The earliest known documented reference in English occurs in an 1869 biography of Gioachino Rossini:
[Rossini] was surrounded to the last by admiring and affectionate friends; and if it be true that, like so many other Italians, he regarded Friday as an unlucky day, and thirteen as an unlucky number, it is remarkable that on Friday, the 13th of November, he died.
One theory states that it is a modern amalgamation of two older superstitions: that thirteen is an unlucky number and that Friday is an unlucky day.
* In numerology, the number twelve is considered the number of completeness, as reflected in the twelve months of the year, twelve signs of the zodiac, twelve hours of the clock, twelve tribes of Israel, twelve Apostles of Jesus, twelve gods of Olympus, etc., whereas the number thirteen was considered irregular, transgressing this completeness. There is also a superstition, thought by some to derive from the Last Supper or a Norse myth, that having thirteen people seated at a table will result in the death of one of the diners.
* Friday has been considered an unlucky day at least since the 14th century’s The Canterbury Tales, and many other professions have regarded Friday as an unlucky day to undertake journeys or begin new projects. Black Friday has been associated with stock market crashes and other disasters since the 1800s.It has also been suggested that Friday has been considered an unlucky day because, according to Christian scripture and tradition, Jesus was crucified on a Friday.