multitude vs legion

multitude and legion both are nouns.

Word	Noun	Adjective	Verb	Adverb
multitude	Yes	No	No	No
legion	Yes	Yes	No	No

As nouns, legion is a hyponym of multitude; that is, legion is a word with a more specific, narrower meaning than multitude:

Other hyponyms of multitude include hive, horde, host, herd, ruck.

multitude (noun)	legion (noun)
a large gathering of people	a vast multitude
the common people generally	a large military unit
a large indefinite quantity	association of ex-servicemen
	archaic terms for army

multitude (adjective)	legion (adjective)
	amounting to a large indefinite number