unintelligible

käsittämätön Not intelligible; unable to be understood.
*1697, (w), Letter to the Bishop of Worcester (second reply):

And indeed, my lord, there are so many passages in your writing in this controversy with me, which for their construction, as well as otherwise, are so unintelligible to me, that if I should be so unmannerly as to measure your understanding by mine, I should not know what to think of them.