Heptadekaphobia

Heptakaidekaphobia (from the Ancient Greek hepta meaning "seven", kai meaning "and", deka meaning "ten", since 7+10=17), or simply heptadekaphobia, is the fear of the number 17. The fear may have originated from Italy, where 17 is considered the unlucky number. Italy is also where the Roman numeral was patented, which the Roman numeral for 17 is XVII, which anagrammically translates to vixi, the Latin word for "I have lived", which in the perfect sense means "my life is over". The fear can also be originated from mythology where died on the 17th day of the month. These imply that the number 17 may believably be a death number.

There are some personal causes of heptakaidekaphobia, including frequently having horrible days on the 17th of the month, e.g. having really bad day on January 17, then February 17, and so on. Some sufferers would have their fears enhanced when full moon occurred on the 17th of the month, which the legend goes back to the death of Osiris during the full moon. Few other sufferers may only fear the full moon falling on the 17th day of the month, which will next occur in June 2019, which would be the subtractive mestoselenophobia-heptakaidekaphobia hybrid, meaning those sufferers would only fear the full moon when falling on the 17th while only fearing the number when full moon falls on it.

The unluckiness of the number 17 may not be that surprising as it is the sum of 4 (the unlucky number in Japan) and 13 (the unlucky number throughout the world).

Heptadekaphobia was mentioned in one of the Jeopardy! clues on July 29, 2014.