schwa vs murmur vowel

schwa and murmur vowel both are nouns.

Word	Noun	Adjective	Verb	Adverb
schwa	Yes	No	No	No
murmur vowel	Yes	No	No	No

As nouns, murmur vowel is a hyponym of schwa; that is, murmur vowel is a word with a more specific, narrower meaning than schwa:

schwa: a neutral middle vowel; occurs in unstressed syllables
murmur vowel: a schwa that is incidental to the pronunciation of a consonant

Other hyponyms of schwa include murmur.

schwa (noun)	murmur vowel (noun)
a neutral middle vowel; occurs in unstressed syllables	a schwa that is incidental to the pronunciation of a consonant