The American Heritage® Dictionary of the English Language, 4th Edition
n. A sound that has the quality of one of the high vowels, as (ē) or (o͞o), and that functions as a consonant before or after vowels, as the initial sounds of yell and well and the final sounds of coy and cow. Also called glide.
n. A sound in speech which has some qualities of a consonant and some qualities of a vowel
n. A letter which represents a semivowel sound, such as w or y in English.
the GNU version of the Collaborative International Dictionary of English
n. A sound intermediate between a vowel and a consonant, or partaking of the nature of both, as in the English w and y.
n. The sign or letter representing such a sound.
The Century Dictionary and Cyclopedia
n. A half-vowel; a sound partaking of the nature of both a vowel and a consonant; an articulation lying near the line of division between vowel and consonant, and so capable of being used with either value; also, the sign representing such a sound.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a vowellike sound that serves as a consonant
Word Usage
"And, Iūnō is the *Latin* name; Uni is the Etruscan which, lo and behold, avoids the word-initial semivowel /j/."