Iota

Iota /aɪˈoʊtə/ (uppercase Ι, lowercase ι; Greek: Ιώτα) is the ninth letter of the Greek alphabet. It was derived from the Phoenician letter Yodh. Letters that arose from this letter include the Latin I and J and the Cyrillic І (І, і), Yi (Ї, ї), Je (Ј, ј), and iotated letters (e.g. Yu (Ю, ю)).

In the system of Greek numerals iota has a value of 10.

Iota represents the sound [i]. In ancient Greek it occurred in both long [iː] and short [i] versions, but this distinction was lost in Koine Greek.

Iota participated as the second element in falling diphthongs, with both long and short vowels as the first element. Where the first element was long, the iota was lost in pronunciation at an early date, and was written in polytonic orthography as iota subscript, in other words as a very small ι under the main vowel, for instance ᾼ ᾳ ῌ ῃ ῼ ῳ. The former diphthongs became digraphs for simple vowels in Koine Greek.

...
Wikipedia