Triskaidekaphobia

Yet, despite beliefs that triskaidekaphobia began long ago and has been passed down through the centuries, the earliest known reference to Friday the 13th as a dreaded day did not appear until 1913. It is merely a 20th century invention.

The great Austrian-American composer Arnold Schoenberg had such a severe case of triskaidekaphobia (the fear of the number 13), he omitted numbering the 13th measure in some of his later works, substituting it with the notation “12a.”

There’s even a name to describe the irrational dread of the date: paraskevidekatriaphobia — a specialized form of triskaidekaphobia, a fear of the number 13.