reduced vowel vs vowel sound

reduced vowel and vowel sound both are nouns.

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

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

Other hypernyms of reduced vowel include vowel.

reduced vowel (noun)	vowel sound (noun)
an unstressed, central variant of a fuller vowel.	a speech sound made with the vocal tract open