pessimism vs disposition

pessimism and disposition both are nouns.

Word	Noun	Adjective	Verb	Adverb
pessimism	Yes	No	No	No
disposition	Yes	No	No	No

As nouns, disposition is a hypernym of pessimism; that is, disposition is a word with a broader meaning than pessimism:

pessimism: a general disposition to look on the dark side and to expect the worst in all things
disposition: your usual mood

Other hypernyms of pessimism include temperament.

pessimism (noun)	disposition (noun)
a general disposition to look on the dark side and to expect the worst in all things	the act or means of getting rid of something
the feeling that things will turn out badly	your usual mood
	a natural or acquired habit or characteristic tendency in a person or thing
	an attitude of mind especially one that favors one alternative over others