Yiddish is mostly a dialect of German, with a bunch of Hebrew thrown in for flavor, along with bits and pieces from other languages.

Like many other German dialects, Yiddish developed out of Middle High German. While the grammar is mainly Germanic, the vocabulary has a large amount of (mainly religious terms) from loshen-koydesh (holy languages) of Hebrew and Aramaic; there are also traces of Romance languages (e.g., tsholnt[/i] 'stew' is related to the French word chaud for 'hot'. There are also quite a few Slavic words. Although Yiddish started out in North-Eastern France and Germany it spread to Eastern Europe (Poland, Ukraine, Lithuania, Romania, and Hungary). Western Yiddish (Netherlands, Germany, Northern France) died out because Western Jews assimilated in the 19th century and adopted the spoken standard languages in their respective countries.

For people used to the Sephardic pronunciation of Hebrew, most of these Hebrew-Aramaic terms sound very different from the traditional Ashkenazic pronunciation of the same terms in Yiddish. Examples such as Seph. H. shabbát vs. Ash H shábes 'Sabbath, Saturday', toráh vs tóyre. There are even dialectal differences within Eastern Yiddish: Polish Y git 'good' vs Lithuanian Y gut (cf. German gut.

The term "Yiddish" is in itself a variant of the German word for "Jewish."

True. The Yiddish word yidish 'Jewish' is related to the German word jüdisch.

Ceci n'est pas un seing.