nerves vs self-possession

nerves and self-possession both are nouns.

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

As nouns, self-possession is a hypernym of nerves; that is, self-possession is a word with a broader meaning than nerves:

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

nerves (noun)	self-possession (noun)
control of your emotions	the trait of resolutely controlling your own behavior
an uneasy psychological state