nonplus

The English Language by David Crystalの中に英国人の著者が米国旅行に行った時の経験が書かれていました。
Having asked for ham and eggs, the question 'How would you like your eggs?' left him nonplussed, as he was unaware of the linguistic (let alone the culinary) possibilities expected of him - such as (immediately learned, due to hunger) once over easy and sunny-side up. Culture-specific phrases of this kind are often absent from dictionaries, and they are very numerous.
イギリス人でこのありさまなので、日本人が英語を学ぶ場合にはもっと多くの疑問が出てくるのは当然ですが、文化の違いが分かった時は面白いとも思います。
ところで "nonplussed" は初めて見る単語なので、最初に "nonpluss" をOneLookで検索したらWordcraft Dictionary しかリストに出てきませんがそこでの説明は "to perplex; to bewilder; to put at a loss of what to do" とあり、納得ですが、"nonplussed" の正しい原型は "nonplus" と気が付き検索し直すとどの辞書にもある単語でした。
OneLook Quick Definitions: be a mystery or bewildering to
Dictionary.com: to render utterly perplexed; puzzle completely.
語源はOnline Etymology Dictionaryによると "properly "state where 'nothing more' can be done or said," from L. non plus "no more, no further." The verb meaning "to bring to a nonplus, to perplex" is attested from 1591".
とありましたがいま一つピンときません。　それこそ "I am nonplussed." であります。