Metaphony

• Progressive metaphony, in which a vowel towards the beginning of a word influences a subsequent vowel.
• Regressive metaphony, in which a vowel towards the end of the word influences a preceding vowel.

• Vowel harmony is sometimes used synonymously with metaphony. Usually, however, "vowel harmony" refers specifically to a synchronic process operating in a particular language, normally requiring all vowels in a word to agree in a particular feature. Most commonly, the triggering vowel is in the first syllable of the word, as in Turkish, Finnish or Hungarian. In some cases, however, the triggering vowel is in the last syllable, typically a suffix, as in many varieties of Andalusian Spanish.
• Umlaut refers to regressive metaphony, usually specifically of a diachronic type operating in the history of a language. The term "umlaut" is found especially in the Germanic languages. In some other languages, other terms are used instead for the same process.