frustration vs letdown

frustration and letdown both are nouns.

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

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

frustration: the feeling that accompanies an experience of being thwarted in attaining your goals
letdown: a feeling of dissatisfaction that results when your expectations are not realized

Other hypernyms of frustration include disappointment.

frustration (noun)	letdown (noun)
an act of hindering someone's plans or efforts	a feeling of dissatisfaction that results when your expectations are not realized
the feeling that accompanies an experience of being thwarted in attaining your goals
a feeling of annoyance at being hindered or criticized