A prothetic vowel is a sound that is added at the beginning of a word to make it easier to pronounce. It is also known as an initial vowel or an initial syllable. Some synonyms for this term include epenthetic vowel, prefix vowel, and formal vowel. An epenthetic vowel is a sound that is added to a word to break up a string of consonants that are hard to pronounce together. A prefix vowel is a vowel that is added to the beginning of a word to give it a different meaning. A formal vowel is a vowel that is added to the beginning of a word to make it sound more formal or sophisticated.