close vowel vs vowel

close vowel and vowel both are nouns.

Word	Noun	Adjective	Verb	Adverb
close vowel	Yes	No	No	No
vowel	Yes	No	No	No

As nouns, vowel is a hypernym of close vowel; that is, vowel is a word with a broader meaning than close vowel:

close vowel: a vowel sound made with your tongue near the top of your mouth.
vowel: a speech sound made with the vocal tract open

Other hypernyms of close vowel include vowel sound.

close vowel (noun)	vowel (noun)
a vowel sound made with your tongue near the top of your mouth.	a speech sound made with the vocal tract open
	a letter of the alphabet standing for a spoken vowel