any one of eight primary, purportedly invariant, sustained vowel sounds that constitute a reference set for describing the vowel inventory of a language.
any one of the eight or more supplementary or secondary cardinal vowels.
Origin of cardinal vowel
First recorded in 1920–25
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British Dictionary definitions for cardinal vowels
a set of theoretical vowel sounds, based on the shape of the mouth needed to articulate them, that can be used to classify the vowel sounds of any speaker in any language
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012