Cool, I'd only seen dekatriaphobia '13-phobia' before.

Coined by a modern Greek no doubt. The word paraskeue: 'preparation' is used in the NT (Mk xv.42, Jo xix.14, 31; Lk xxiii.54) to mean the day of preparation before the Sabbath. Now the Sabbath starts on Friday evening and ends on Saturday evening, so paraskeue: would run from Thursday sundown to Friday sundown. Approximately our Friday, I suppose.