letdown vs disappointment

letdown and disappointment both are nouns.

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

As nouns, letdown and disappointment are synonyms defined as:

letdown and disappointment: a feeling of dissatisfaction that results when your expectations are not realized

letdown (noun)	disappointment (noun)
a feeling of dissatisfaction that results when your expectations are not realized	an act (or failure to act) that disappoints someone
	a feeling of dissatisfaction that results when your expectations are not realized