UPDATED: This article was originally titled "[friggatriskaidekaphobia], a word that means "fear of Friday the thirteenth".
It is based on the term [triskaidekaphobia] which means "fear of the number thirteen". Although in modern Greek the number thirteen is pronounced [dekatria] (δεκατρία), the term triskaideka means "three and ten" in older Greek. Add the Greek suffix [φοβία] [phobia] meaning "fear" and you have the word triskaidekaphobia. An alternate spelling is triskadekaphobia
The term [Frigga] refers to a Norse goddess after whom the name for the day Friday originates. Frigga is the wife of Odin and the mother (or stepmother, depending on who interprets old traditions) of Thor.
Reading the book "Complications: Notes from the Life of a Young Surgeon" by Atul Awande. MD (one of the books in my library) I came across a synonym for this concept, the word "paraskevidekatriaphobia" also written as "paraskevideikatriaphobia". The author does not explain the origin or etymology of the term. What he does say is that in the United States, on Friday the 13th, people "perform rituals before leaving the house, call in sick to work, or postpone flights or major purchases, causing businesses to lose $750 million annually". Keep in mind that this book was written in 2002. A simple calculation at https://www.inflationtool.com/ shows that by 2022, this corresponds to 1.2 billion dollars!
The origin of the superstition that Friday the 13th is a bad day started on Friday the 13th, 1307. On this date all the Knights Templar were rounded, arrested, accused, tortured, and executed. It is indeed a bad day, but only if you are a member of the Knights Templar!