The close-mid front rounded vowel, or high-mid front rounded vowel, is a type of vowel sound, used in some spoken languages. Acoustically it is a close-mid front-central rounded vowel. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ø⟩, a lowercase letter o with a diagonal stroke through it, derived from the Danish, Norwegian and Faroese alphabets which use the letter to represent this sound. The symbol is commonly referred to as "o, slash" in English.
The IPA prefers terms "close" and "open" for vowels, and the name of the article follows this. However, a large number of linguists,[who?] perhaps a majority, prefer the terms "high" and "low".
Its vowel backness is front, which means the tongue is positioned as far forward as possible in the mouth without creating a constriction that would be classified as a consonant. Note that rounded front vowels are often centralized, which means that often they are in fact near-front.
Its roundedness is compressed, which means that the margins of the lips are tense and drawn together in such a way that the inner surfaces are not exposed.
Catford notes that most languages with rounded front and back vowels use distinct types of labialization, protruded back vowels and compressed front vowels. However, a few languages, such as Scandinavian ones, have protruded front vowels. One of these, Swedish, even contrasts the two types of rounding in front vowels (see near-close near-front rounded vowel, with Swedish examples of both types of rounding).
As there are no diacritics in the IPA to distinguish protruded and compressed rounding, an old diacritic for labialization, ⟨ ̫⟩, will be used here as an ad hoc symbol for protruded front vowels. Another possible transcription is ⟨øʷ⟩ or ⟨eʷ⟩ (a close-mid front vowel modified by endolabialization), but this could be misread as a diphthong.
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