When someone has not an iota of something, they have none of it — not even the smallest piece. You almost always meet the word in a no-sentence: not an iota of proof, not one iota of difference. It sounds a little formal, a little bookish, the kind of phrase a teacher or a newspaper uses when they want to sound firm. Everyday talk more often says “not a bit” or “none at all.” Though actually, iota began as a letter: it is the smallest letter in the Greek alphabet (Ι, ι). A line in the New Testament said that not one iota would pass from the law, and English kept the word for “the tiniest bit.” People also say not one jot; that is the same old idea by another path. There is a completely different IOTA in some legal money talk — interest on a trust account — usually written in capitals. That is office language, not the tiny-bit word, and not one most students need day to day.