possessor vs part-owner

possessor and part-owner both are nouns.

Word	Noun	Adjective	Verb	Adverb
possessor	Yes	No	No	No
part-owner	Yes	No	No	No

As nouns, part-owner is a hyponym of possessor; that is, part-owner is a word with a more specific, narrower meaning than possessor:

Other hyponyms of possessor include holder, homeowner, householder, saver, shipowner.

possessor (noun)	part-owner (noun)
a person who owns something	a person who owns something in common with others