Paramnesia: noun [par-am-nee-zhuh]
1. Psychiatry: a disorder of memory where fact and fantasy are confused
2. the inability to remember the meanings of common words
Where I found this word: Joseph Heller's Catch-22, page 204. According to Heller there are three types of paramnesia: deja vu (seen before), jamais vu (never seen), and presque vu (almost seen).
Usage: "The subtle, recurring confusion between illusion and reality that was characteristic of paramnesia fascinated the chaplain, and he knew a number of things about it."
I really enjoy this word, but I have to admit that my favorite word I've found in my reading still has to be "poleaxed:" see post from October 3, 2006. Or not, I'm just sayin', poleaxed is still my fav.