oral vowel vs vowel

oral vowel and vowel both are nouns.

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

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

oral vowel: (linguistics) an ordinary vowel that is produced without nasalization.
vowel: a speech sound made with the vocal tract open

Other hypernyms of oral vowel include vowel sound.

oral vowel (noun)	vowel (noun)
(linguistics) an ordinary vowel that is produced without nasalization.	a speech sound made with the vocal tract open
	a letter of the alphabet standing for a spoken vowel