I, too, had only ever encountered the "tris..."-word in regard to fear-of-Friday-the-13th; I'd never seen the "para.."-word until now.

I understand and agree with Michael's opinion that a calendar date like Friday the 13th is too artificial ("man-made") to possibly mean anything on a supernatural plane. But then again, since I don't really believe any of this stuff anyway, I don't supoe my opinion counts for much...

Incidentally, the reason I've always heard for the association of the number 13 with bad luck is that there were 13 people present at the Last Supper (Jesus plus 12 apostles). Insofar as this might be true, at least for some European/Christian cultures, the association with Friday probably dates all the way back to the origins of the "13" superstition, Friday being the day of the Crucifixion.