Magen David vs emblem

Magen David and emblem both are nouns.

Word	Noun	Adjective	Verb	Adverb
Magen David	Yes	No	No	No
emblem	Yes	No	No	No

As nouns, emblem is a hypernym of Magen David; that is, emblem is a word with a broader meaning than Magen David:

Magen David: a six-pointed star formed from two equilateral triangles; an emblem symbolizing Judaism
emblem: a visible symbol representing an abstract idea

Other hypernyms of Magen David include allegory, hexagram.

Magen David (noun)	emblem (noun)
a six-pointed star formed from two equilateral triangles; an emblem symbolizing Judaism	special design or visual object representing a quality, type, group, etc.
	a visible symbol representing an abstract idea