fear of the number 13
About the word:
Every Friday the 13th, lookups on triskaidekaphobia spike on Merriam-Webster.com.
The word comes from the Greek word for thirteen and the New Latin word "phobia."
The origin of this fear is murky. Some trace it to ancient Hindu beliefs, others to Norse mythology, and still others to the Last Supper, after which Jesus was betrayed by one of the thirteen people present. Interestingly enough, known mention of the fear of thirteen in print dates back only to the late 1800s.