mass meeting vs assemblage

mass meeting and assemblage both are nouns.

Word	Noun	Adjective	Verb	Adverb
mass meeting	Yes	No	No	No
assemblage	Yes	No	No	No

As nouns, assemblage is a hypernym of mass meeting; that is, assemblage is a word with a broader meaning than mass meeting:

Other hypernyms of mass meeting include assembly, gathering.

mass meeting (noun)	assemblage (noun)
a large gathering of people intended to arouse enthusiasm	the social act of assembling
	a system of components assembled together for a particular purpose
	a group of persons together in one place
	several things grouped together or considered as a whole