nonplus [nɒnˈplʌs, ˈnɒnplʌs] v. t.
1.) To put at a loss as to what to think, say, or do; bewilder.
1.) A state of perplexity, confusion, or bewilderment (American Heritage Dictionary of the English Language).
Etymology: From Latin non plus, no more : non, not + plus, more.
" Larry: Yeah, what's going on?
Jeff: I sponsored a kid from the inner city to go to a summer camp.
Larry: You sponsored an inner city kid?
Jeff: An underprivileged kid, yeah.
Larry: You're kidding.
Larry: I'm completely...nonplussed. Is that the right word?
Jeff: I don't know what the right word is. I'm flabbergasted and I'll tell you why: he set fire to the canteen and his cabin. Who does that?!" (Curb Your Enthusiasm, Larry David, 2000).