[как + PrepP; these forms only; subj-compl with copula (subj: human)]
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⇒ one is completely lacking in comprehension or understanding of sth.:
- X is all (completely) at sea;
- X is totally lost.
♦ Сочинения [Кирилл! писал посредственно, почерк ужасен, в математике соображал слабо... Английский язык? Ну, разве что. В детстве силой заставляли ходить в английскую группу... Но ведь только лексика, а в грамматике - как в лесу (Трифонов 5). His [Kirill's] school compositions were mediocre, his handwriting abominable, and he was weak in math . His knowledge of English? Well, that at least was something. When he was a child we had forced him to join an English language group. But even so, all he had was a large vocabulary. When it came to grammar, he was completely in the dark (5a).
♦ "Выслушайте же до конца, но только не умом: я боюсь вашего ума; сердцем лучше: может быть, оно рассудит, что у меня нет матери, что я была как в лесу..." (Гончаров 1). "Hear me out, then, but not with your intellect - I'm afraid of your intellect-better with your heart, perhaps it will realize that I have no mother, that I was completely at sea. " (1a).
Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. С.И. Лубенская. 2004.