pessimism vs temperament

pessimism and temperament both are nouns.

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

As nouns, temperament is a hypernym of pessimism; that is, temperament 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
temperament: your usual mood

Other hypernyms of pessimism include disposition.

pessimism (noun)	temperament (noun)
a general disposition to look on the dark side and to expect the worst in all things	an adjustment of the intervals (as in tuning a keyboard instrument) so that the scale can be used to play in different keys
the feeling that things will turn out badly	your usual mood
	excessive emotionalism or irritability and excitability (especially when displayed openly)