nonplussed 
April 30, 2006 | 08:56

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