retention vs ownership

retention and ownership both are nouns.

Word	Noun	Adjective	Verb	Adverb
retention	Yes	No	No	No
ownership	Yes	No	No	No

As nouns, ownership is a hypernym of retention; that is, ownership is a word with a broader meaning than retention:

Other hypernyms of retention include possession.

retention (noun)	ownership (noun)
the act of retaining something	the act of having and controlling property
the power of retaining liquid	the relation of an owner to the thing possessed; possession with the right to transfer possession to others
the power of retaining and recalling past experience	the state or fact of being an owner