What is ninth letter of greek alphabet?

The ninth letter of the Greek alphabet is called "Iota" (ι). It corresponds to the English letter "I" and has a numerical value of 10 in the Greek system of numerals.

In ancient Greek, Iota was pronounced like the English "ee" sound, but in modern Greek, it is pronounced like the English "i" sound (like in "bit").

Iota is often used as a prefix to denote something small or insignificant, as in the English word "iota" itself, which means a tiny amount.

In mathematics, Iota is used as a symbol to represent the imaginary unit, which is the square root of -1. In this context, it is often written as "i" with a lower case letter to distinguish it from the letter "l".

In Greek mythology, Iota (or Iotaia) was a nymph who lived on the island of Kos and was said to have been the mother of the god Asclepius, the god of healing.