semivowel definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a vowel-like sound occurring in consonantal positions in the same syllable with a true vowel, characterized by brief duration and rapid change from one position of articulation to another: the English glides (w) and (y) are semivowels
semivowel definition by American Heritage Dictionary
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.