Dictionary.com/nonplussed:

nonplussed (NON-plussed) adjective

filled with bewilderment; "at a loss to understand those remarks"; "puzzled that she left without saying goodbye" [syn: at a loss(p), nonplused, puzzled]

Source: WordNet ® 2.0, © 2003 Princeton University

My choice this week is a word that is becoming quite misunderstood of late, as can be demonstrated at The Mavens' Word of the Day.