possession vs self-possession

possession and self-possession both are nouns.

Word	Noun	Adjective	Verb	Adverb
possession	Yes	No	No	No
self-possession	Yes	No	No	No

As nouns, possession and self-possession are synonyms defined as:

possession and self-possession: the trait of resolutely controlling your own behavior

Other synonyms of possession include self-command, self-control, self-will, will power, willpower.

possession (noun)	self-possession (noun)
anything owned or possessed	the trait of resolutely controlling your own behavior
the act of having and controlling property
(sport) the act of controlling the ball (or puck)
the trait of resolutely controlling your own behavior
a territory that is controlled by a ruling state
a mania restricted to one thing or idea
being controlled by passion or the supernatural