A thematic vowel, also known as a connecting vowel, is a type of vowel that is added to the root word in many languages to connect it with the rest of the word. In some languages, such as Greek, this vowel is called a "vowel of the theme" or "theme vowel." Other synonyms for thematic vowel include auxiliary vowel, morphological vowel, inflectional vowel, and flexional vowel. Its purpose is to show certain grammatical changes in the word, such as tense, voice, and mood. Understanding the role of the thematic vowel is important in learning the grammar and structure of many languages, especially those with complex inflectional systems.