Definition: Noun. Fear of the number 13.
Etymology: From the Greek tris (“three”) and kai (“and”) and deka (“ten”) and phobia (“fear”). The first use of the word was by Isador Coriat’s in his textbook, Abnormal Psychology, in 1910. Triskaidekaphobia is often used to refer to the specific fear of Friday the 13th; however this fear has its own term, more daunting than the aforementioned: paraskevidekatriaphobia. Related: triskaidekaphilia: obsession with the number 13.
Bad luck falling on Friday the 13th is one of the most well-known and enduring superstitions. Nathaniel Lachenmeyer has written the definitive investigation into the number, appropriately titled: 13: The Number of the World’s Most Popular Superstition. There are many explanations about the sources of this superstition, but three are the most common. The first comes from the 16th century, when it was believed that the covens of witches had 13 members. The second is from mythology — the story of Odin. Odin, the chief of the Norse gods, held a banquet in Valhalla for a dozen people. Loki, a trickster giant, showed up as the 13th guest and killed the god Balder to reduce the guest list back to 12. However the source of this story, Lokasenna, contradicts some of these details: the banquet was held by Aegir, there were 18 guests (including Loki), and the murder of Balder did not take place there. The third and most prevalent theory is based on the fact that there were 13th guests at the last supper — Jesus and 12 disciples. Also, according to the New Testament, the crucifixion occurred on a Friday.
Up until the 20th century, there is no explicit mention of bad luck on Friday the 13th. There are two notable publications: one was an obscure, but heavily promoted, novel by Thomas Lawson, Friday, the Thirteenth (1907), and the other was the publication of a letter in a newspaper, Notes and Queries (1913) that mentions “the evil luck of Friday the 13th.”