What is ninth letter in the greek alphabet?

The ninth letter in the Greek alphabet is called "Iota" or "Ι" in uppercase and "ι" in lowercase. It is pronounced as a short "i" sound in English, similar to the "i" in "bit" or "sit".

In ancient Greek, the letter iota was often used as a word-final marker, indicating the end of a word. It was also used as a numeral, representing the number ten in the Greek numeric system.

In mathematics, the letter iota is commonly used to represent the imaginary unit, which is the square root of negative one. This is denoted as "i" in algebraic notation, and is used extensively in complex analysis and other branches of mathematics.

In Christianity, iota is also significant as it is mentioned in the New Testament (Matthew 5:18), where Jesus says, "For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished." This passage is often interpreted to mean that even the smallest detail of God's law must be followed and fulfilled.