nonplus \non-PLUHS\, transitive verb:
To cause to be at a loss as to what to think, say, or do; to
confound; to perplex; to bewilder.
But I could see in his little blinking eyes that my success
had nonplussed him.
--Ferdinand Mount, [1]Jem (and Sam)
I told him that to many people she is one of the best
sculptors alive, but he seemed nonplussed by the thought.
--Jed Perl, [2]Eyewitness: Reports From an Art World in
Crisis
She had grown a good deal in the last six months, and an
amount of thinking had gone on in that young head which
would have astonished him greatly could he have known it
all, for Rose was one of the children who observe and
meditate much, and now and then nonplus their friends by a
wise or curious remark.
--Louisa May Alcott, [3]Eight Cousins
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Nonplus is from the Latin non plus, "no more." To be
nonplussed is to be at a point where "no more" can be said or
done.