In phonetics and phonology, a semivowel or glide is a sound that is phonetically similar to a vowel sound but functions as the syllable boundary, rather than as the nucleus of a syllable. Examples of semivowels in English are the consonants y and w, in yes and west, respectively. Written w/ in IPA, y and w are near to the vowels ee and oo in seen and moon, written uː/ in IPA. The term glide may alternatively refer to any type of transitional sound, not necessarily a semivowel.
In the International Phonetic Alphabet, the diacritic attached to non-syllabic vowel letters is an inverted breve placed below the symbol representing the vowel: U+032F ̯COMBINING INVERTED BREVE BELOW. When there is no room for the tack under a symbol, it may be written above, using U+0311 ̑COMBINING INVERTED BREVE. Before 1989, non-syllabicity was represented by U+0306 ̆COMBINING BREVE, which now stands for extra-shortness.
Additionally, there are dedicated symbols for four semivowels that correspond to the four close cardinal vowel sounds:
In addition, some authors consider the rhotic approximants [ɹ], [ɻ ] to be semivowels corresponding to R-colored vowels such as [ɚ]. As mentioned above, the labiodental approximant[ʋ] is considered a semivowel in some treatments. An unrounded central semivowel, [ ȷ̈ ], equivalent to [ɨ], is uncommon, though rounded [ẅ] (or [w̟]), equivalent to [ʉ], is found in Swedish and Norwegian.