Bewildered; unsure how to respond or act.(adjective)
Unfazed, unaffected, or unimpressed.(adjective)
Simple past tense and past participle of nonplus.(verb)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "nonplussed" in a sentence
"Nevertheless, to be perfectly accurate, I was using the word nonplussed obtusely if not downright inccorrectly."
"Also, cycling fans got to witness another milestone today, when BSNYC commentator Eben Oliver Weiss typed the word "nonplussed" for the one millionth time during his daily blog."
"At least your expression would not have been "nonplussed" as it appears all Portlanders, Portlandonians, Portlandites?"