Iota (Ι ι) is the 9th letter of the Greek alphabet and has a numeric value of 10.

The word iota is also used in English to express a very small amount. By some accounts this usage stems from the third- and fourth-century theological dispute over the Arian doctrine that Jesus and God the Father were of distinct but similar substances -- Greek homoi-ousios -- against the orthodox doctrine that they are one substance -- Greek homo-ousios. The two words differ by one iota.