will power vs self-possession

will power and self-possession both are nouns.

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

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

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

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

will power (noun)	self-possession (noun)
the trait of resolutely controlling your own behavior	the trait of resolutely controlling your own behavior