semivowel: a vowel sound which functions as a consonant; that is, some other vowel is the loudest, central sound in the syllable. The semivowel corresponding to i is y, and the one corresponding to u is w. Semivowels are usually shorter than normal vowels and are almost always high [1] vowels. Semivowels are also sometimes called semiconsonants. Sometimes what sounds like a semivowel is better analyzed as part of a diphthong. [Spanish: semiconsonante]