n. Fear of the number thirteen.
Composer Arnold Schoenberg, whose treatise on harmony was dedicated to "the hallowed memory of Gustav Mahler," developed a theory of writing music "using 12 tones" and perhaps as a result developed tridecaphobia — a trembling fear of the number 13.
—Kenneth LaFave, “Mahler's Grand Farewell,” The Arizona Republic, November 01, 1998
1996 (earliest)
Queen Saturn XIII, Cindy Larsen, rides atop her giant swan float as the 15-float parade rolls on Napoleon Avenue Wednesday. The parade's theme was 'Tridecaphobia,' which means fear of the number 13.
—“Thirteenth Night” (photo caption), Times-Picayune (New Orleans, LA), February 15, 1996
The more commonly accepted word for the fear of a baker's dozen is triskaidekaphobia (1911). However, I like tridecaphobia because it's much simpler to remember (and to spell!).