hexagram vs Magen David

hexagram and Magen David both are nouns.

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

As nouns, Magen David is a hyponym of hexagram; that is, Magen David is a word with a more specific, narrower meaning than hexagram:

hexagram: a regular polygon formed by extending each of the sides of a regular hexagon to form two equilateral triangles
Magen David: a six-pointed star formed from two equilateral triangles; an emblem symbolizing Judaism

Other hyponyms of hexagram include Mogen David, Shield of David, Solomon's seal, Star of David.

hexagram (noun)	Magen David (noun)
a regular polygon formed by extending each of the sides of a regular hexagon to form two equilateral triangles	a six-pointed star formed from two equilateral triangles; an emblem symbolizing Judaism