High German vs Yiddish

High German and Yiddish both are nouns.

Word	Noun	Adjective	Verb	Adverb
High German	Yes	No	No	No
Yiddish	Yes	No	No	No

As nouns, Yiddish is a hyponym of High German; that is, Yiddish is a word with a more specific, narrower meaning than High German:

High German: the standard German language; developed historically from West Germanic
Yiddish: a dialect of High German including some Hebrew and other words; spoken in Europe as a vernacular by many Jews; written in the Hebrew script

High German (noun)	Yiddish (noun)
the standard German language; developed historically from West Germanic	a dialect of High German including some Hebrew and other words; spoken in Europe as a vernacular by many Jews; written in the Hebrew script