short vowel vs vowel

short vowel and vowel both are nouns.

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

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

short vowel: In languages that distinguish vowel length, a vowel which is normally pronounced shorter than a long vowel.
vowel: a speech sound made with the vocal tract open

Other hypernyms of short vowel include vowel sound.

short vowel (noun)	vowel (noun)
In languages that distinguish vowel length, a vowel which is normally pronounced shorter than a long vowel.	a speech sound made with the vocal tract open
	a letter of the alphabet standing for a spoken vowel