letdown vs dissatisfaction

letdown and dissatisfaction both are nouns.

Word	Noun	Adjective	Verb	Adverb
letdown	Yes	No	No	No
dissatisfaction	Yes	No	No	No

As nouns, dissatisfaction is a hypernym of letdown; that is, dissatisfaction is a word with a broader meaning than letdown:

letdown: a feeling of dissatisfaction that results when your expectations are not realized
dissatisfaction: the feeling of being displeased and discontent

letdown (noun)	dissatisfaction (noun)
a feeling of dissatisfaction that results when your expectations are not realized	the feeling of being displeased and discontent