»nonplussed

I have been mis-using the word nonplussed for quite some time; like fey, inflammable, and unravelled it means the opposite of what I think it does (the latter two more so than fey, I suppose; I became overly excited about the denotations of fey one day in the eleventh grade, and eventually the teacher removed me from the classroom.)

Nonplussed means "surprised, perplexed to the point of speechlessness":

... The New York Times Manual of Style and Usage: “Nonplused does not mean fazed or unfazed. It means bewildered to the point of speechlessness.” To me, it does (more or less) mean ‘fazed’ but does not mean ‘unfazed’. Despite this confusion, perhaps The New York Times copyeditors should pay more attention to the basically sound advice in their usage book. The fact that this book takes on the topic shows that the meaning of nonplussed has indeed become an issue; the previous edition did not have an entry for this word ... "