Certain Greek vowels are the IOTAS and etas. IOTAS are the fifth letter of the Greek alphabet, while etas are the fourth letter. These two letters are used in the Greek language to represent vowel sounds. They are also used in other languages, such as English, to represent certain vowel sounds. In English, the iota is often used to represent the 'ee' sound, while the eta is used to represent the 'ay' sound.