Слово "abstruse". Англо-русский словарь Мюллера

He had read a great deal, chiefly delighting in books which were unusual; and he poured forth his stores of abstruse knowledge with child-like enjoyment of the amazement of his hearers.

The subject is not so abstruse as I thought it was.

But there were other days when they settled down to their work almost eagerly, making a tremendous show of entering up their minutes and drafting long memoranda which were never finished--when the argument as to what they were supposedly arguing about grew extraordinarily involved and abstruse, with subtle haggling over definitions, enormous digressions, quarrels--threats, even, to appeal to higher authority.

But there were other days when they settled down to their work almost eagerly, making a tremendous show of entering up their minutes and drafting long memoranda which were never finished--when the argument as to what they were supposedly arguing about grew extraordinarily involved and abstruse, with subtle haggling over definitions, enormous digressions, quarrels--threats, even, to appeal to higher authority.

The subject is not so abstruse as I thought it was.

These characters, as any one might readily guess, form a cipher—that is to say, they convey a meaning; but then, from what is known of Kidd, I could not suppose him capable of constructing any of the more abstruse cryptographs.