Greek to me

Unintelligible, as in “I didn't understand a word he said—it was all Greek to me.” Shakespeare said it best in this exchange from Julius Caesar: Cassius: Did Cicero say any thing? Casca: Aye, he spoke Greek. Cassius: To what effect? Casca: Nay, an' I tell you that, I'll ne'er look you i' the face again: but those that understood him smiled at one another and shook their heads; but, for mine own part, it was Greek to me.