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In linguistics, umlaut (from German "sound alteration") is a sound change in which a vowel is pronounced more like a following vowel or semivowel. The term umlaut was originally coined in connection with the study of Germanic languages, as it had occurred prominently in the history of many of them (see Germanic umlaut). While a common English plural is umlauts, the German plural is Umlaute.
Umlaut is a form of assimilation, the process of one speech sound becoming more similar to a nearby sound. If a word has two vowels, one far back in the mouth and the other far forward, it takes more effort to pronounce. If the vowels were closer together, it would take less effort. Thus, one way the language may change is that these two vowels get be drawn closer together.
In the general sense, umlaut is essentially the same as regressive metaphony.
The most commonly seen types of umlaut are the following:
- Vowel raising, triggered by a following high vowel (often specifically a high front vowel such as /i/).
- Vowel fronting, triggered by a following front vowel (often specifically a high front vowel such as /i/).
- Vowel lowering, triggered by a following non-high vowel (often specifically a low vowel such as /a/).
- Vowel rounding, triggered by a following rounded vowel (often specifically a high rounded vowel such as /u/).
These processes may be named by the vowel that triggers the change (for example, i-mutation, a-mutation, u-mutation, sometimes known as i-umlaut, a-umlaut, u-umlaut). However, processes named in this fashion may not have consistent meanings across language families.
All of these processes occurred in the history of the Germanic languages; see Germanic umlaut for more details. I-mutation is the most prominent of the processes, to the extent that it is often referred to simply as "umlaut".