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äu is a digraph used in German orthography, formed by the letter ä (a with diaeresis) followed by u. It denotes a specific vowel sound in German and is among several spellings that represent the same sound in different words.

Phonology and pronunciation

In standard German, äu represents a rounded diphthong that is commonly transcribed as /ɔʏ/ in IPA. In practice, the sound is closely related to the eu combination, and äu and eu often reflect the same pronunciation in many words. Examples include Mäuse (mice) [ˈmɔɪzə], Häuser (houses) [ˈhɔɪzɐ], and läuten (to ring) [ˈlɔɪtən]. The umlauted ä changes the preceding vowel in the root, while the following u helps create the diphthong rather than a simple sequence of vowels.

Orthography and usage

äu is not a separate letter but a two-character sequence. It appears in many common German words and often corresponds to the eu spelling, which yields the same /ɔʏ/ sound in standard German. The occurrence of äu can reflect historic vowel mutation (umlaut) and the interaction between a stem vowel and a following u in various inflected forms, such as plural or verb forms. In multilingual contexts or when umlauts cannot be written, äu is sometimes represented as aeu, though this is a transliteration rather than a standard spelling.

Encoding and variants

In digital text, äu consists of two distinct characters: ä (U+00E4) and u (U+0075). There is no single Unicode code point for a combined äu. The digraph is specific to German and some closely related varieties; in other languages, the letter sequence may have different pronunciations or appear only in loanwords.