slavery vs vassalage

slavery and vassalage both are nouns.

Word	Noun	Adjective	Verb	Adverb
slavery	Yes	No	No	No
vassalage	Yes	No	No	No

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

Other hyponyms of slavery include bonded labor, servitude, serfdom, serfhood.

slavery (noun)	vassalage (noun)
work done under harsh conditions for little or no pay	the state of a serf
the practice of owning slaves
the state of being under the control of another person