semivowel

n. speech sound which has the articulation of a vowel but is treated as a consonant (Phonetics)

Semivowels (also glides, more rarely: semiconsonants) are non-syllabic vowels that form diphthongs with syllabic vowels. They may be contrasted with approximants, which are similar to but closer than vowels or semivowels and behave as consonants. Semivowels are normally written by adding the IPA non-syllabicity mark to a vowel symbol, but often for simplicity the vowel symbol alone is written.
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Noun
1. a vowel-like sound that serves as a consonant
(synonym) glide
(hypernym) phone, speech sound, sound
(hyponym) palatal

(n.)
The sign or letter representing such a sound.
  

(n.)
A sound intermediate between a vowel and a consonant, or partaking of the nature of both, as in the English w and y.
  

semivowel /'semi'vauəl/
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