close vowel vs vowel sound

close vowel and vowel sound both are nouns.

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

As nouns, vowel sound is a hypernym of close vowel; that is, vowel sound 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 sound: a speech sound made with the vocal tract open

Other hypernyms of close vowel include vowel.

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